1. Add a new extension to support creation of immutable textures with
sized internal YUV formats
2. Rename YUV format enums from *_ANGLEX to *_ANGLE
3. Move YUV format enums from angleutils.h to glext_angle.h
Bug: angleproject:5773
Change-Id: Ibfe732f4c9a4a536be56481f33e4768f6227c212
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2820153
Commit-Queue: Mohan Maiya <m.maiya@samsung.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Mohan Maiya