Fix PVRTC1 frontend validation PVRTC1 texture dimensions must always be powers of two. Moreover, Apple hardware requires them to be squares. Bug: angleproject:5731, angleproject:2634 Change-Id: I5fcdc364b37d17b60cf772c21ba38795272236fd Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2741585 Reviewed-by: Kenneth Russell <kbr@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Alexey Knyazev <lexa.knyazev@gmail.com>