This services output capture tasks for the 'framebuffer' and 'full
framebuffer' pixel sources.

Both pixel sources come from the same source: the EGLSurface. The only
difference is the area. The EGLSurface contains the borders used for
output decorations, hence 'full framebuffer' is possible to capture.

We use GL_ANGLE_pack_reverse_row_order extension to make glReadPixels
return the image data in the layout we need for wl_shm buffers directly.
Without the extension we have to flip manually.

Another extension to the same effect is MESA_pack_invert, but this is
not specified for GL ES. It also uses a different token value, so it
cannot be directly substituted even if supported.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>