Add MRT test for foveated rendering feature Bug: angleproject:42266906 Change-Id: Ia98b1a2a0195ec213bc510a3b62c85b0adc630eb Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5763719 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>