Move Parser state into a class of its own.
Move Parser state into a class of its own.

Summary:
Ongoing work to tidy up the `Parser` a little. Currently, a parser instance is both a
long-lived entity that hangs around for the duration of the buckd process and short-
lived entity that exists to service a single command. By moving the state into its own
class, we start to delineate between these responsibilities.

This is the smallest change I can make --- a follow up diff will move the state to a
top-level class of its own.

Test Plan: buck test --all

vschs007/buck,rowillia/buck,illicitonion/buck,kageiit/buck,rhencke/buck,zhuxiaohao/buck,grumpyjames/buck,siddhartharay007/buck,LegNeato/buck,darkforestzero/buck,LegNeato/buck,hgl888/buck,daedric/buck,rhencke/buck,daedric/buck,liuyang-li/buck,rowillia/buck,MarkRunWu/buck,SeleniumHQ/buck,darkforestzero/buck,brettwooldridge/buck,rmaz/buck,saleeh93/buck-cutom,zhuxiaohao/buck,rhencke/buck,dushmis/buck,LegNeato/buck,Distrotech/buck,Learn-Android-app/buck,Distrotech/buck,kageiit/buck,mnuessler/buck,grumpyjames/buck,artiya4u/buck,ilya-klyuchnikov/buck,rmaz/buck,stuhood/buck,zpao/buck,tgummerer/buck,justinmuller/buck,darkforestzero/buck,clonetwin26/buck,luiseduardohdbackup/buck,mogers/buck,daedric/buck,brettwooldridge/buck,neonichu/buck,OkBuilds/buck,bocon13/buck,lukw00/buck,Learn-Android-app/buck,janicduplessis/buck,shybovycha/buck,shs96c/buck,ilya-klyuchnikov/buck,sdwilsh/buck,vine/buck,facebook/buck,JoelMarcey/buck,illicitonion/buck,liuyang-li/buck,stuhood/buck,daedric/buck,shybovycha/buck,nguyentruongtho/buck,ilya-klyuchnikov/buck,clonetwin26/buck,mnuessler/buck,shs96c/buck,k21/buck,bocon13/buck,mnuessler/buck,ilya-klyuchnikov/buck,stuhood/buck,Addepar/buck,daedric/buck,Learn-Android-app/buck,marcinkwiatkowski/buck,marcinkwiatkowski/buck,mogers/buck,Addepar/buck,Addepar/buck,1yvT0s/buck,dpursehouse/buck,rhencke/buck,zpao/buck,liuyang-li/buck,romanoid/buck,davido/buck,sdwilsh/buck,OkBuilds/buck,Distrotech/buck,illicitonion/buck,romanoid/buck,vine/buck,zhuxiaohao/buck,hgl888/buck,SeleniumHQ/buck,k21/buck,siddhartharay007/buck,vschs007/buck,neonichu/buck,artiya4u/buck,dushmis/buck,stuhood/buck,Distrotech/buck,JoelMarcey/buck,vschs007/buck,grumpyjames/buck,Heart2009/buck,dsyang/buck,sdwilsh/buck,ilya-klyuchnikov/buck,janicduplessis/buck,OkBuilds/buck,shs96c/buck,grumpyjames/buck,Dominator008/buck,LegNeato/buck,janicduplessis/buck,robbertvanginkel/buck,zhan-xiong/buck,dushmis/buck,pwz3n0/buck,LegNeato/buck,davido/buck,pwz3n0/buck,Dominator008/buck,rmaz/buck,daedric/buck,pwz3n0/buck,raviagarwal7/buck,dsyang/buck,liuyang-li/buck,hgl888/buck,JoelMarcey/buck,OkBuilds/buck,marcinkwiatkowski/buck,LegNeato/buck,brettwooldridge/buck,rowillia/buck,brettwooldridge/buck,mogers/buck,neonichu/buck,darkforestzero/buck,zpao/buck,JoelMarcey/buck,pwz3n0/buck,liuyang-li/buck,nguyentruongtho/buck,justinmuller/buck,zhan-xiong/buck,artiya4u/buck,grumpyjames/buck,justinmuller/buck,bocon13/buck,zhuxiaohao/buck,dsyang/buck,bocon13/buck,mogers/buck,Distrotech/buck,sdwilsh/buck,nguyentruongtho/buck,zhan-xiong/buck,romanoid/buck,raviagarwal7/buck,vschs007/buck,raviagarwal7/buck,dsyang/buck,artiya4u/buck,lukw00/buck,ilya-klyuchnikov/buck,rowillia/buck,neonichu/buck,zhan-xiong/buck,rmaz/buck,siddhartharay007/buck,mikekap/buck,zhuxiaohao/buck,dsyang/buck,davido/buck,Addepar/buck,zhuxiaohao/buck,dsyang/buck,mogers/buck,Learn-Android-app/buck,bocon13/buck,rowillia/buck,justinmuller/buck,rowillia/buck,facebook/buck,JoelMarcey/buck,lukw00/buck,artiya4u/buck,luiseduardohdbackup/buck,davido/buck,sdwilsh/buck,sdwilsh/buck,ilya-klyuchnikov/buck,grumpyjames/buck,ilya-klyuchnikov/buck,vine/buck,SeleniumHQ/buck,1yvT0s/buck,rowillia/buck,Addepar/buck,shybovycha/buck,bocon13/buck,Dominator008/buck,darkforestzero/buck,zhuxiaohao/buck,liuyang-li/buck,k21/buck,artiya4u/buck,justinmuller/buck,sdwilsh/buck,marcinkwiatkowski/buck,Dominator008/buck,robbertvanginkel/buck,facebook/buck,LegNeato/buck,hgl888/buck,illicitonion/buck,robbertvanginkel/buck,mogers/buck,rhencke/buck,brettwooldridge/buck,brettwooldridge/buck,Distrotech/buck,MarkRunWu/buck,vine/buck,neonichu/buck,shybovycha/buck,rowillia/buck,justinmuller/buck,Dominator008/buck,mread/buck,rowillia/buck,dushmis/buck,robbertvanginkel/buck,hgl888/buck,robbertvanginkel/buck,saleeh93/buck-cutom,janicduplessis/buck,darkforestzero/buck,romanoid/buck,davido/buck,rmaz/buck,Distrotech/buck,clonetwin26/buck,daedric/buck,raviagarwal7/buck,vschs007/buck,davido/buck,shybovycha/buck,davido/buck,mread/buck,k21/buck,vine/buck,luiseduardohdbackup/buck,illicitonion/buck,dsyang/buck,facebook/buck,kageiit/buck,vine/buck,zhuxiaohao/buck,SeleniumHQ/buck,robbertvanginkel/buck,vschs007/buck,artiya4u/buck,k21/buck,justinmuller/buck,Heart2009/buck,rmaz/buck,raviagarwal7/buck,zhan-xiong/buck,davido/buck,Heart2009/buck,zhuxiaohao/buck,darkforestzero/buck,zpao/buck,grumpyjames/buck,OkBuilds/buck,Learn-Android-app/buck,OkBuilds/buck,neonichu/buck,clonetwin26/buck,shybovycha/buck,shs96c/buck,dushmis/buck,shs96c/buck,k21/buck,liuyang-li/buck,rmaz/buck,siddhartharay007/buck,siddhartharay007/buck,raviagarwal7/buck,sdwilsh/buck,rmaz/buck,vschs007/buck,illicitonion/buck,Learn-Android-app/buck,vine/buck,tgummerer/buck,1yvT0s/buck,1yvT0s/buck,Dominator008/buck,stuhood/buck,facebook/buck,Learn-Android-app/buck,zhan-xiong/buck,Addepar/buck,Learn-Android-app/buck,grumpyjames/buck,saleeh93/buck-cutom,robbertvanginkel/buck,tgummerer/buck,OkBuilds/buck,mikekap/buck,mread/buck,illicitonion/buck,Addepar/buck,JoelMarcey/buck,daedric/buck,ilya-klyuchnikov/buck,JoelMarcey/buck,shs96c/buck,robbertvanginkel/buck,dushmis/buck,Distrotech/buck,dpursehouse/buck,dushmis/buck,OkBuilds/buck,vine/buck,mogers/buck,mogers/buck,romanoid/buck,siddhartharay007/buck,mread/buck,luiseduardohdbackup/buck,illicitonion/buck,dushmis/buck,artiya4u/buck,ilya-klyuchnikov/buck,mread/buck,grumpyjames/buck,lukw00/buck,justinmuller/buck,sdwilsh/buck,marcinkwiatkowski/buck,mogers/buck,davido/buck,hgl888/buck,raviagarwal7/buck,tgummerer/buck,brettwooldridge/buck,shs96c/buck,daedric/buck,Addepar/buck,bocon13/buck,brettwooldridge/buck,shs96c/buck,zhan-xiong/buck,marcinkwiatkowski/buck,clonetwin26/buck,stuhood/buck,tgummerer/buck,dushmis/buck,janicduplessis/buck,Learn-Android-app/buck,mikekap/buck,JoelMarcey/buck,marcinkwiatkowski/buck,OkBuilds/buck,shybovycha/buck,romanoid/buck,SeleniumHQ/buck,lukw00/buck,zhan-xiong/buck,k21/buck,shybovycha/buck,LegNeato/buck,romanoid/buck,Distrotech/buck,Heart2009/buck,Heart2009/buck,dpursehouse/buck,dsyang/buck,raviagarwal7/buck,LegNeato/buck,stuhood/buck,k21/buck,janicduplessis/buck,dsyang/buck,artiya4u/buck,LegNeato/buck,luiseduardohdbackup/buck,vschs007/buck,marcinkwiatkowski/buck,LegNeato/buck,darkforestzero/buck,1yvT0s/buck,rmaz/buck,mnuessler/buck,OkBuilds/buck,pwz3n0/buck,Dominator008/buck,LegNeato/buck,clonetwin26/buck,tgummerer/buck,dpursehouse/buck,OkBuilds/buck,rhencke/buck,janicduplessis/buck,clonetwin26/buck,rhencke/buck,shybovycha/buck,raviagarwal7/buck,grumpyjames/buck,mikekap/buck,zhan-xiong/buck,clonetwin26/buck,luiseduardohdbackup/buck,lukw00/buck,SeleniumHQ/buck,pwz3n0/buck,JoelMarcey/buck,1yvT0s/buck,romanoid/buck,neonichu/buck,stuhood/buck,justinmuller/buck,hgl888/buck,romanoid/buck,dsyang/buck,luiseduardohdbackup/buck,bocon13/buck,robbertvanginkel/buck,kageiit/buck,OkBuilds/buck,dsyang/buck,davido/buck,vine/buck,robbertvanginkel/buck,Heart2009/buck,artiya4u/buck,illicitonion/buck,JoelMarcey/buck,raviagarwal7/buck,pwz3n0/buck,MarkRunWu/buck,mnuessler/buck,shs96c/buck,OkBuilds/buck,1yvT0s/buck,rowillia/buck,MarkRunWu/buck,Heart2009/buck,bocon13/buck,JoelMarcey/buck,robbertvanginkel/buck,marcinkwiatkowski/buck,tgummerer/buck,kageiit/buck,justinmuller/buck,Addepar/buck,Addepar/buck,grumpyjames/buck,liuyang-li/buck,mnuessler/buck,dsyang/buck,k21/buck,grumpyjames/buck,liuyang-li/buck,mogers/buck,clonetwin26/buck,illicitonion/buck,k21/buck,brettwooldridge/buck,SeleniumHQ/buck,bocon13/buck,darkforestzero/buck,shs96c/buck,k21/buck,JoelMarcey/buck,illicitonion/buck,ilya-klyuchnikov/buck,sdwilsh/buck,shs96c/buck,janicduplessis/buck,vschs007/buck,davido/buck,shybovycha/buck,Addepar/buck,k21/buck,lukw00/buck,brettwooldridge/buck,vschs007/buck,daedric/buck,Distrotech/buck,brettwooldridge/buck,mnuessler/buck,1yvT0s/buck,mikekap/buck,darkforestzero/buck,clonetwin26/buck,vschs007/buck,SeleniumHQ/buck,raviagarwal7/buck,zpao/buck,tgummerer/buck,stuhood/buck,siddhartharay007/buck,mikekap/buck,MarkRunWu/buck,mread/buck,pwz3n0/buck,lukw00/buck,raviagarwal7/buck,mikekap/buck,raviagarwal7/buck,marcinkwiatkowski/buck,lukw00/buck,marcinkwiatkowski/buck,Dominator008/buck,shs96c/buck,bocon13/buck,neonichu/buck,artiya4u/buck,davido/buck,facebook/buck,stuhood/buck,clonetwin26/buck,mnuessler/buck,hgl888/buck,darkforestzero/buck,vine/buck,daedric/buck,tgummerer/buck,tgummerer/buck,janicduplessis/buck,illicitonion/buck,JoelMarcey/buck,Addepar/buck,robbertvanginkel/buck,janicduplessis/buck,nguyentruongtho/buck,romanoid/buck,MarkRunWu/buck,mikekap/buck,marcinkwiatkowski/buck,kageiit/buck,SeleniumHQ/buck,pwz3n0/buck,dpursehouse/buck,Learn-Android-app/buck,stuhood/buck,dushmis/buck,nguyentruongtho/buck,rhencke/buck,dpursehouse/buck,saleeh93/buck-cutom,daedric/buck,liuyang-li/buck,mikekap/buck,ilya-klyuchnikov/buck,rmaz/buck,dpursehouse/buck,Dominator008/buck,Distrotech/buck,romanoid/buck,lukw00/buck,saleeh93/buck-cutom,dsyang/buck,saleeh93/buck-cutom,clonetwin26/buck,MarkRunWu/buck,MarkRunWu/buck,zpao/buck,zhan-xiong/buck,luiseduardohdbackup/buck,robbertvanginkel/buck,nguyentruongtho/buck,justinmuller/buck,pwz3n0/buck,tgummerer/buck,clonetwin26/buck,marcinkwiatkowski/buck,luiseduardohdbackup/buck,pwz3n0/buck,facebook/buck,illicitonion/buck,zhan-xiong/buck,sdwilsh/buck,SeleniumHQ/buck,siddhartharay007/buck,zhan-xiong/buck,romanoid/buck,sdwilsh/buck,rmaz/buck,darkforestzero/buck,lukw00/buck,neonichu/buck,mikekap/buck,brettwooldridge/buck,justinmuller/buck,zhan-xiong/buck,k21/buck,Learn-Android-app/buck,romanoid/buck,janicduplessis/buck,daedric/buck,siddhartharay007/buck,mnuessler/buck,rowillia/buck,janicduplessis/buck,rmaz/buck,nguyentruongtho/buck,dpursehouse/buck,Heart2009/buck,davido/buck,justinmuller/buck,SeleniumHQ/buck,Dominator008/buck,hgl888/buck,mikekap/buck,rowillia/buck,darkforestzero/buck,shybovycha/buck,Heart2009/buck,liuyang-li/buck,kageiit/buck,1yvT0s/buck,sdwilsh/buck,SeleniumHQ/buck,vschs007/buck,mogers/buck,Dominator008/buck,Addepar/buck,bocon13/buck,Dominator008/buck,mikekap/buck,ilya-klyuchnikov/buck,brettwooldridge/buck,rhencke/buck,vschs007/buck,zpao/buck,rhencke/buck,rmaz/buck,vine/buck,rhencke/buck,SeleniumHQ/buck,shs96c/buck,shybovycha/buck,LegNeato/buck,shybovycha/buck