GL: Use a valid internal format for CopyTexImage in BlitGL::blitColorBufferWithShader
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 <682bdb9e7d8ba359ef169b8db374e7a99d394a46@google.com>
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Commit-Queue: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>

ppy/angle,ppy/angle,ppy/angle,ppy/angle