If a texture or renderbuffer needs to be cleared for robust access or
due to having emulated channels, it is immediately cleared.  The former
relies on a front-end feature that optimizes robust access clears only
to levels and layers that are not fully initialized through data upload.

Bug: angleproject:2722
Change-Id: Icdab856eb4ffe963f78569b6d80d9ff5cb27ff9b
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1535056
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>