WIP: Implement GL_ANGLE_framebuffer_blit

Adam Jackson requested to merge ajax/mesa:gl-angle-framebuffer-blit into main

A strict GLES2 subset of EXT_framebuffer_blit. Mesa supports the EXT version unconditionally, so the additional restrictions are added by checking explicitly for GLES 2.0.

Not quite done yet, need to write the check that z/s blits copy the entire buffer (post-scissor), and should quote the spec explicitly. But hey, it compiles.

Merge request reports