Add AHB clear tests using glClearTexImage * Add tests to clear AHB images before readback, but using glClearTexImage() instead of using a framebuffer and glClear() * AHBClearAppliedViaClearTexImageBeforeReadBack * AHBTwiceClearViaClearTexImageAppliedBeforeReadBack Bug: b/223456677 Change-Id: Ic5ad2b5202aa24f38dc1783205900a0dab5125f9 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6299797 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Amirali Abdolrashidi <abdolrashidi@google.com>