Dawn: update for API changes (Buffer).

CreateBufferMapped() is now CreateBuffer() with a mappedAtCreation flag.
MapReadAsync() and MapWriteAsync() are now MapAsync().

Change-Id: I98e8513ed9acf73515b7960d437c1fde5e80c03a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/306536
Commit-Queue: Stephen White <senorblanco@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
2 files changed