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.

servers/rendering/renderer_canvas_render.h

@@ -545,6 +545,7 @@ public:
 	virtual void update() = 0;
 
 	virtual void set_debug_redraw(bool p_enabled, double p_time, const Color &p_color) = 0;
+	virtual uint32_t get_pipeline_compilations(RS::PipelineSource p_source) = 0;
 
 	RendererCanvasRender() {
 		ERR_FAIL_COND_MSG(singleton != nullptr, "A RendererCanvasRender singleton already exists.");