Move StdSteadyClock to skgpu (in new GpuTypesPriv.h file)

I want to use the same type in Graphite.

Bug: Bug: b/239604347
Change-Id: I034c397f5d95fb37b14af33b62ee09dc7aeabb20
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/671058
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
14 files changed