Add Graphite variants of *VkRenderEngine, *GpuContext, & *BackendTexture

GraphiteVkRenderEngine is currently unused, but I've tested it locally
by modifying SkiaVkRenderEngine::create

Test: manual validation (unused, will add to tests soon)
Bug: b/293371537
Change-Id: I961a40e5073bd5452886c486e2ce19b62a7b12a7
10 files changed