shell: Always track focus state per workspace
shell: Always track focus state per workspace

It's a little simpler than always creating and destroying it when we
switch workspace, and we'll need the focus_state soon.

Tarnyko/weston-xdg_surface_present,giucam/weston,Gnurou/weston,Fantu/compositor-spice,sir-murray/weston,xorgy/weston,giucam/weston,kwm81/weston,jonnylamb/weston,jonnylamb/weston,Fantu/compositor-spice,mchalupa/weston,eyolfson/weston,mchalupa/weston,eyolfson/weston,Fantu/compositor-spice,Gnurou/weston,sir-murray/weston,Tarnyko/weston-xdg_surface_present,udoprog/weston,kwm81/weston,udoprog/weston,krezovic/weston,krezovic/weston,xorgy/weston