[graphite] Make stencil-and-cover stencil settings accessible

This is in preparation for additional tessellation-based RenderSteps.

Cq-Include-Trybots: luci.skia.skia.primary:Test-Mac12-Clang-MacBookPro16.2-GPU-IntelIrisPlus-x86_64-Debug-All-Graphite,Test-Mac11-Clang-MacMini9.1-GPU-AppleM1-arm64-Release-All-Graphite,Test-Mac11-Clang-MacMini9.1-GPU-AppleM1-arm64-Debug-All-ASAN_Graphite,Test-Mac10.15.7-Clang-MacBookPro11.5-GPU-RadeonHD8870M-x86_64-Debug-All-Graphite,Perf-Mac11-Clang-MacMini9.1-GPU-AppleM1-arm64-Release-All-Graphite,Perf-Mac10.15.7-Clang-MacBookPro11.5-GPU-RadeonHD8870M-x86_64-Release-All-Graphite,Build-Mac-Clang-x86_64-Release-Graphite,Build-Mac-Clang-x86_64-Debug-Graphite,Build-Mac-Clang-arm64-Release-iOS_Graphite,Build-Mac-Clang-arm64-Release-Graphite,Build-Mac-Clang-arm64-Debug-iOS_Graphite,Build-Mac-Clang-arm64-Debug-Graphite_NoGpu,Build-Mac-Clang-arm64-Debug-Graphite,Build-Mac-Clang-arm64-Debug-ASAN_Graphite
Bug: skia:12703
Change-Id: I497ea14802201be10535ee26147838b28ab6b34d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/521957
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
3 files changed