This MR implements support for
EGL_KHR_partial_update. The partial_update extension allows us to inform the GL implementation ahead of time which areas of the buffer we are going to be rendering to. Doing so allows tiled renderers to skip reloading old content into the tile buffer in some cases, improving performance by lowering memory bandwidth.
In the process, some unnecessarily cryptic parts of GL renderer's output have been cleaned up to make it more clear and explicit, in particular as we twist and turn through a number of different co-ordinate spaces and definitions of 'damage'.
Tested on Panfrost's implementation, which has not yet been merged.
Fixes: #134 (closed)