WebGL: Add 3D tex copying feedback loop detection. When copying to and from the same texture, we need to reject only the feedback loops formed with the same levels of the texture - copying between different unrelated layers and levels is fine. This change also fixes a couple bugs in our D3D11 CopyTexSubImage3D implementation. We were missing some "!" operators, and we actually would hit an ASSERT when trying to blit from a level of a 3D texture. BUG=angleproject:1685 Change-Id: Id715bebafe8336cf8bb95d0d06275a8b95e522e1 Reviewed-on: https://chromium-review.googlesource.com/425494 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org>