Draft: glamor: use glBlit where possible
When we're simply doing a blit, using glBlitFramebuffer gives more information to the GL driver about what our intent is and can optionally enable optimizations (eg: do a copy instead of a draw).
The main use case I have for this is 'present_copy_region' (which calls into glamor_copy_area and utltimately this function).
For now glBlit usage is stricter than required (eg: single src/dst box), and could be extended later if it proves useful.
Signed-off-by: Pierre-Eric Pelloux-Prayer pierre-eric.pelloux-prayer@amd.com