GL: Use a valid internal format for CopyTexImage in BlitGL::blitColorBufferWithShader The frontend format is not always valid to use for glCopyTexImage. Translate it to a valid format for the current driver. TEST=deqp/functional/gles3/framebufferblit/default_framebuffer_00.html BUG=angleproject:4632 Change-Id: I838a1b27b528f074f440575adb88357a910f596a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2196842 Reviewed-by: Jonah Ryan-Davis <jonahr@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>