This change does not support reinterpreted formats yet.  Additionally,
despite lack of support for RGB32 formats, EXT_texture_buffer is exposed
by this extension.  Those formats don't support the STORAGE_TEXEL_BUFFER
feature on any known hardware.

Bug: angleproject:3573
Change-Id: I85f45eb23f6a0aa533488bb98d9f226d59af4d76
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2534395
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>