Extend validation to allow texture rectangle-backed textures as
blitFramebuffer sources and destinations.
Add end-to-end test covering this functionality, and run the
IOSurfaceClientBufferTests against both ES2 and ES3.
Bug: angleproject:3669
Change-Id: I7b8815a2c98072c12de45717afbba9e9b29ba253
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1694483
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
