ddl: add ReOrgHandle to support resume column ddl reorg job.
ddl: add ReOrgHandle to support resume column ddl reorg job.

zimulala/tidb,kyle-wang/tidb,pingcap/tidb,c4pt0r/tidb,silenceper/tidb,pingcap/tidb,JinheLin/tidb,ngaut/tidb,tiancaiamao/tidb,wusphinx/tidb,mccxj/tidb,gaocegege/tidb,XuHuaiyu/tidb,anywhy/tidb,qhsong/tidb,kyle-wang/tidb,myrice/tidb,myrice/tidb,simon-xia/tidb,liyu4/tidb,pingcap/tidb,pingcap/tidb,ngaut/tidb,coocood/tidb,c4pt0r/tidb,spongedu/tidb,qiuyesuifeng/tidb,kyle-wang/tidb,ngaut/tidb,ngaut/tidb,c4pt0r/tidb,Nify/tidb,andelf/tidb,qhsong/tidb,gaocegege/tidb,cosmtrek/tidb,liyu4/tidb,zimulala/tidb,Cofyc/tidb,simon-xia/tidb,CodeRushing/tidb,astaxie/tidb,ngaut/tidb,c4pt0r/tidb,wusphinx/tidb,Cofyc/tidb,astaxie/tidb,coocood/tidb,cosmtrek/tidb,qiuyesuifeng/tidb,pingcap/tidb,ngaut/tidb,yangwenmai/tidb,c4pt0r/tidb,anywhy/tidb,8cbx/tidb,ming-relax/tidb,8cbx/tidb,louishust/tidb,louishust/tidb,ueizhou/tidb,yuanwhy/tidb,yangwenmai/tidb,silentred/tidb,zs634134578/tidb,silentred/tidb,tiancaiamao/tidb,zs634134578/tidb,andelf/tidb,XuHuaiyu/tidb,Nify/tidb,silenceper/tidb,yuanwhy/tidb,EvilMcJerkface/tidb,spongedu/tidb,JinheLin/tidb,ueizhou/tidb,mccxj/tidb,ming-relax/tidb,kyle-wang/tidb,kyle-wang/tidb,kyle-wang/tidb,CodeRushing/tidb,EvilMcJerkface/tidb,pingcap/tidb,c4pt0r/tidb