[Graphite] Store Mtl queue on QueueManager instead of SharedContext.

Bug: b/239822490
Change-Id: Ic4695f0d54257bf87328f3f34b74438d13ab40bd
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/568798
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
14 files changed