compose: Extract set_focus().
compose: Extract set_focus().

Most of the code here was in show_box(), but we also pull in the
call to get_focus_area() from compose.start().

andersk/zulip,Galexrt/zulip,Galexrt/zulip,kou/zulip,punchagan/zulip,showell/zulip,eeshangarg/zulip,mahim97/zulip,jrowan/zulip,ryanbackman/zulip,tommyip/zulip,j831/zulip,amanharitsh123/zulip,synicalsyntax/zulip,verma-varsha/zulip,christi3k/zulip,christi3k/zulip,jackrzhang/zulip,rht/zulip,eeshangarg/zulip,jackrzhang/zulip,synicalsyntax/zulip,j831/zulip,hackerkid/zulip,timabbott/zulip,jphilipsen05/zulip,shubhamdhama/zulip,christi3k/zulip,jphilipsen05/zulip,verma-varsha/zulip,j831/zulip,shubhamdhama/zulip,rishig/zulip,Galexrt/zulip,zulip/zulip,shubhamdhama/zulip,punchagan/zulip,amanharitsh123/zulip,synicalsyntax/zulip,synicalsyntax/zulip,SmartPeople/zulip,Galexrt/zulip,dhcrzf/zulip,kou/zulip,brockwhittaker/zulip,zulip/zulip,hackerkid/zulip,amanharitsh123/zulip,brainwane/zulip,eeshangarg/zulip,rishig/zulip,ryanbackman/zulip,rht/zulip,vabs22/zulip,andersk/zulip,andersk/zulip,punchagan/zulip,jrowan/zulip,eeshangarg/zulip,tommyip/zulip,kou/zulip,timabbott/zulip,vaidap/zulip,mahim97/zulip,hackerkid/zulip,rht/zulip,jackrzhang/zulip,ryanbackman/zulip,j831/zulip,showell/zulip,jrowan/zulip,vaidap/zulip,tommyip/zulip,Galexrt/zulip,vabs22/zulip,brainwane/zulip,timabbott/zulip,brainwane/zulip,ryanbackman/zulip,mahim97/zulip,dhcrzf/zulip,andersk/zulip,amanharitsh123/zulip,jackrzhang/zulip,brainwane/zulip,punchagan/zulip,verma-varsha/zulip,vaidap/zulip,brainwane/zulip,dhcrzf/zulip,rishig/zulip,eeshangarg/zulip,showell/zulip,jphilipsen05/zulip,brainwane/zulip,dhcrzf/zulip,vaidap/zulip,dhcrzf/zulip,tommyip/zulip,SmartPeople/zulip,j831/zulip,showell/zulip,tommyip/zulip,christi3k/zulip,rishig/zulip,jackrzhang/zulip,jackrzhang/zulip,punchagan/zulip,vabs22/zulip,kou/zulip,rishig/zulip,amanharitsh123/zulip,jrowan/zulip,mahim97/zulip,rht/zulip,rishig/zulip,zulip/zulip,hackerkid/zulip,brockwhittaker/zulip,vaidap/zulip,kou/zulip,synicalsyntax/zulip,synicalsyntax/zulip,jrowan/zulip,vaidap/zulip,zulip/zulip,verma-varsha/zulip,tommyip/zulip,jackrzhang/zulip,timabbott/zulip,verma-varsha/zulip,eeshangarg/zulip,shubhamdhama/zulip,j831/zulip,jphilipsen05/zulip,zulip/zulip,showell/zulip,rishig/zulip,christi3k/zulip,SmartPeople/zulip,dhcrzf/zulip,punchagan/zulip,amanharitsh123/zulip,brockwhittaker/zulip,ryanbackman/zulip,andersk/zulip,showell/zulip,tommyip/zulip,brockwhittaker/zulip,Galexrt/zulip,SmartPeople/zulip,punchagan/zulip,andersk/zulip,jphilipsen05/zulip,SmartPeople/zulip,vabs22/zulip,hackerkid/zulip,showell/zulip,rht/zulip,andersk/zulip,verma-varsha/zulip,hackerkid/zulip,brainwane/zulip,kou/zulip,zulip/zulip,Galexrt/zulip,synicalsyntax/zulip,kou/zulip,jphilipsen05/zulip,mahim97/zulip,SmartPeople/zulip,shubhamdhama/zulip,shubhamdhama/zulip,vabs22/zulip,ryanbackman/zulip,hackerkid/zulip,vabs22/zulip,rht/zulip,zulip/zulip,jrowan/zulip,brockwhittaker/zulip,timabbott/zulip,timabbott/zulip,mahim97/zulip,eeshangarg/zulip,shubhamdhama/zulip,christi3k/zulip,brockwhittaker/zulip,timabbott/zulip,rht/zulip,dhcrzf/zulip