[Vulkan] Gracefully fail on copy if a target format is unsupported

src/xenia/gpu/vulkan/texture_cache.h

@@ -47,6 +47,7 @@ class TextureCache {
     VmaAllocation alloc;
     VmaAllocationInfo alloc_info;
     VkFramebuffer framebuffer;  // Blit target frame buffer.
+    VkImageUsageFlags usage_flags;
 
     uintptr_t access_watch_handle;
     bool pending_invalidation;