Migrate metal tools away from GrContext

Change-Id: I73a73ca5d088c35acd23be3336d8d1e3e859a82e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/318760
Commit-Queue: Brian Salomon <bsalomon@google.com>
Auto-Submit: Adlai Holler <adlai@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
5 files changed