Add GL_MESA_framebuffer_flip_x and GL_MESA_framebuffer_swap_xy (#390)

GL_MESA_framebuffer_swap_xy and GL_MESA_framebuffer_flip_x are used
together with GL_MESA_framebuffer_flip_y to implement the
pre-rotation feature.

Co-authored-by: Cici Ruan <cuicuiruan@google.com>
15 files changed