Added support for cached text drawing in View2D. Cache is needed to
prevent the viewmatrix being set/restored on each text drawing.
Adding a string:
void UI_view2d_text_cache_add(View2D *v2d, float x, float y, char *str)
Drawing:
void UI_view2d_text_cache_draw(ARegion *ar)
Nothing else needed; just make sure cache-draw is always called at end
of a view2d drawing function, to clear cache memory.
On todo for next: a version with a rectf boundary to clip text within.
cb96aa47db