editor: Add support for selection
editor: Add support for selection

Make it possible to select text and render the selection to the editor
example.

Signed-off-by: Jan Arne Petersen <8c3575d1e692bfe9fd3220cb3956503cdd270f15@openismus.com>

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