This is a reland of 1c3bea4593
Original change's description:
> Set up eGPU/discrete support for MacOS.
>
> Pulled out of https://skia-review.googlesource.com/c/skia/+/271319.
>
> For Metal, will default to an eGPU or discrete GPU if one is available.
> For GL, will attempt to use a Radeon eGPU, and will fallback
> if one can't be found.
>
> Change-Id: I0a1efb3afca612ac75be56f633d811dda68f9d10
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/277516
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Jim Van Verth <jvanverth@google.com>
Change-Id: I1f9dcbf82465533ae8bce96b5cc73a7c627071a4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/277696
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
d29d885c88