Implement asynchronous transfer queues, thread guards on RenderingDevice. Add ubershaders and rework pipeline caches for Forward+ and Mobile.

- Implements asynchronous transfer queues from PR #87590.
- Adds ubershaders that can run with specialization constants specified as push constants.
- Pipelines with specialization constants can compile in the background.
- Added monitoring for pipeline compilations.
- Materials and shaders can now be created asynchronously on background threads.
- Meshes that are loaded on background threads can also compile pipelines as part of the loading process.

editor/editor_resource_preview.cpp

@@ -131,7 +131,7 @@ Variant EditorResourcePreviewGenerator::DrawRequester::_post_semaphore() const {
 }
 
 bool EditorResourcePreview::is_threaded() const {
-	return RSG::texture_storage->can_create_resources_async();
+	return RSG::rasterizer->can_create_resources_async();
 }
 
 void EditorResourcePreview::_thread_func(void *ud) {