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/dummy/rasterizer_canvas_dummy.h

@@ -56,6 +56,7 @@ public:
 	void update() override {}
 
 	virtual void set_debug_redraw(bool p_enabled, double p_time, const Color &p_color) override {}
+	virtual uint32_t get_pipeline_compilations(RS::PipelineSource p_source) override { return 0; }
 
 	RasterizerCanvasDummy() {}
 	~RasterizerCanvasDummy() {}