Add layout flags for pixel formats.

At this CL, we can now parse the qualifiers and have layout flags
for them, but they are not permitted anywhere, so the only thing
they can do is generate an error. In followup CLs, we will permit
them on storage-texture declarations.

These layout qualifiers aren't actually required in Metal, but will
be required for storage-texture support in WGSL and SPIR-V.

Bug: b/295161016
Change-Id: Ibf2be5a42fd4f9504c672aa1c5fa6faef901edd2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/739076
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
7 files changed