Make GM::onGpuSetup take a GrDirectContext

This should, hopefully, clarify the role of onGpuSetup vis a vis onDraw.

The remaining tools are updated in:
https://skia-review.googlesource.com/c/skia/+/300220/ (Update remaining tools to GrDirectContext)

Change-Id: I19d6eec4d16cb9ebad8924763a18225cc871f0f2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/300172
Reviewed-by: Adlai Holler <adlai@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
15 files changed