editor: Extract text handling into text_layout
editor: Extract text handling into text_layout

Create a text_layout struct and functions for handling simple text
layouts.

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

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