This CL merges the StorageAccess enum with the AccessControl enum. The
enum is moved up to src/ast and placed in its own file for clarity.
Change-Id: I95a905a399b5d2e046ea1ea429b35f2064510c2d
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/31242
Commit-Queue: David Neto <dneto@google.com>
Reviewed-by: David Neto <dneto@google.com>
