GL_EXT_read_format_bgra support
GL_EXT_read_format_bgra support

Implemented DetermineBGRAReadFormatSupport in order to allow enabling
readFormat when possible with the Vulkan backend.

While reading the spec, I realized that ANGLE only seems to care
about BGRA8888 and not the new types mentioned in the extension.
Logged a new issue (http://anglebug.com/4302) to track this.

Bug: angleproject:4294
Change-Id: I071ed89574de9b4088df2301c317d3769cb31ce6
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2003237
Commit-Queue: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@chromium.org>
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>

ppy/angle,ppy/angle,ppy/angle,ppy/angle