Allow BGRA -> RGBA for glCopyTex[Sub]Image The opposite RGBA->BGRA was already allowed for handling platform- specific default framebuffers. This allows the copying a IOSurface- backed framebuffers to RGBA textures. Bug: chromium:1523778 Change-Id: I124a4acc8c8fcdd1d3aae861d756d17022c4b4cc Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5254778 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>