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
diff --git a/libs/renderengine/skia/VulkanInterface.h b/libs/renderengine/skia/VulkanInterface.h
index 512e62c..2824fcb 100644
--- a/libs/renderengine/skia/VulkanInterface.h
+++ b/libs/renderengine/skia/VulkanInterface.h
@@ -23,6 +23,10 @@
 
 using namespace skgpu;
 
+namespace skgpu {
+struct VulkanBackendContext;
+} // namespace skgpu
+
 namespace android {
 namespace renderengine {
 namespace skia {
@@ -39,8 +43,8 @@
     void init(bool protectedContent = false);
     void teardown();
 
-    // TODO: b/293371537 - Graphite variant (external/skia/include/gpu/vk/VulkanBackendContext.h)
     GrVkBackendContext getGaneshBackendContext();
+    VulkanBackendContext getGraphiteBackendContext();
     VkSemaphore createExportableSemaphore();
     VkSemaphore importSemaphoreFromSyncFd(int syncFd);
     int exportSemaphoreSyncFd(VkSemaphore semaphore);