Add SkiaVk backend to RenderEngine

This CL adds a new backend, SkiaVk, to RenderEngine.

The new functionality is to create a Vulkan device/instance (possibly
protected) and handle flush/waitFence via VkSemaphores fed to
GrBackendSemaphores.

+ make ctors of GLES/Vk RE's private so as to ensure GrContexts are
  created

Test: atest librenderengine_test
Bug: 236390072

Change-Id: I69119623b194885bcc4cf2ddc8e592576b713b19
diff --git a/libs/renderengine/benchmark/RenderEngineBench.cpp b/libs/renderengine/benchmark/RenderEngineBench.cpp
index d44eb46..bd7b617 100644
--- a/libs/renderengine/benchmark/RenderEngineBench.cpp
+++ b/libs/renderengine/benchmark/RenderEngineBench.cpp
@@ -39,6 +39,10 @@
             return "skiaglthreaded";
         case RenderEngine::RenderEngineType::SKIA_GL:
             return "skiagl";
+        case RenderEngine::RenderEngineType::SKIA_VK:
+            return "skiavk";
+        case RenderEngine::RenderEngineType::SKIA_VK_THREADED:
+            return "skiavkthreaded";
         case RenderEngine::RenderEngineType::GLES:
         case RenderEngine::RenderEngineType::THREADED:
             LOG_ALWAYS_FATAL("GLESRenderEngine is deprecated - why time it?");