Allow glCopyTexImage2D from BGRX and RGBX to GL_LUMINANCE glCopyTexImage2D was failing with GL_INVALID_OPERATION when copying from GL_RGBX8_ANGLE buffer to GL_LUMINANCE texture, while it should be supported. Also updated validator to allow copying from RGBX & BGRX to GL_RED_EXT, GL_RG_EXT. Bug: chromium:1269826 Change-Id: I865dcdd46921730968995822d71ba34b39e49262 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3439129 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>