Feed all top-level GPU accessors through skgpu::BaseDevice (take 2)

This pulls the GPU-specific accessors off of SkCanvas and SkDevice - moving them all to skgpu::BaseDevice and SkCanvasPriv.

This will allow us to more easily change the gpu class hierarchy (esp. changing GrSurfaceDrawContext to skgpu::v1:SurfaceDrawContext) w/o churning the public API.

TBR=brianosman@google.com
Bug: skia:11837
Change-Id: Ib69a3ea27c840fa7758bc3318395a27228c7ae9d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/431539
Reviewed-by: Robert Phillips <robertphillips@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
18 files changed