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

- Implements asynchronous transfer queues from PR godotengine#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.

Author: DarioSamo

doc/classes/Performance.xml

@@ -224,7 +224,22 @@
 		<constant name="NAVIGATION_OBSTACLE_COUNT" value="33" enum="Monitor">
 			Number of active navigation obstacles in the [NavigationServer3D].
 		</constant>
-		<constant name="MONITOR_MAX" value="34" enum="Monitor">
+		<constant name="PIPELINE_COMPILATIONS_CANVAS" value="34" enum="Monitor">
+			Number of pipeline compilations that were triggered by the 2D canvas renderer.
+		</constant>
+		<constant name="PIPELINE_COMPILATIONS_MESH" value="35" enum="Monitor">
+			Number of pipeline compilations that were triggered by loading meshes. These compilations will show up as longer loading times the first time a user runs the game and the pipeline is required.
+		</constant>
+		<constant name="PIPELINE_COMPILATIONS_SURFACE" value="36" enum="Monitor">
+			Number of pipeline compilations that were triggered by building the surface cache before rendering the scene. These compilations will show up as a stutter when loading an scene the first time a user runs the game and the pipeline is required.
+		</constant>
+		<constant name="PIPELINE_COMPILATIONS_DRAW" value="37" enum="Monitor">
+			Number of pipeline compilations that were triggered while drawing the scene. These compilations will show up as stutters during gameplay the first time a user runs the game and the pipeline is required.
+		</constant>
+		<constant name="PIPELINE_COMPILATIONS_SPECIALIZATION" value="38" enum="Monitor">
+			Number of pipeline compilations that were triggered to optimize the current scene. These compilations are done in the background and should not cause any stutters whatsoever.
+		</constant>
+		<constant name="MONITOR_MAX" value="39" enum="Monitor">
 			Represents the size of the [enum Monitor] enum.
 		</constant>
 	</constants>

doc/classes/RenderingServer.xml

@@ -5687,6 +5687,39 @@
 		<constant name="RENDERING_INFO_VIDEO_MEM_USED" value="5" enum="RenderingInfo">
 			Video memory used (in bytes). When using the Forward+ or mobile rendering backends, this is always greater than the sum of [constant RENDERING_INFO_TEXTURE_MEM_USED] and [constant RENDERING_INFO_BUFFER_MEM_USED], since there is miscellaneous data not accounted for by those two metrics. When using the GL Compatibility backend, this is equal to the sum of [constant RENDERING_INFO_TEXTURE_MEM_USED] and [constant RENDERING_INFO_BUFFER_MEM_USED].
 		</constant>
+		<constant name="RENDERING_INFO_PIPELINE_COMPILATIONS_CANVAS" value="6" enum="RenderingInfo">
+			Number of pipeline compilations that were triggered by the 2D canvas renderer.
+		</constant>
+		<constant name="RENDERING_INFO_PIPELINE_COMPILATIONS_MESH" value="7" enum="RenderingInfo">
+			Number of pipeline compilations that were triggered by loading meshes. These compilations will show up as longer loading times the first time a user runs the game and the pipeline is required.
+		</constant>
+		<constant name="RENDERING_INFO_PIPELINE_COMPILATIONS_SURFACE" value="8" enum="RenderingInfo">
+			Number of pipeline compilations that were triggered by building the surface cache before rendering the scene. These compilations will show up as a stutter when loading an scene the first time a user runs the game and the pipeline is required.
+		</constant>
+		<constant name="RENDERING_INFO_PIPELINE_COMPILATIONS_DRAW" value="9" enum="RenderingInfo">
+			Number of pipeline compilations that were triggered while drawing the scene. These compilations will show up as stutters during gameplay the first time a user runs the game and the pipeline is required.
+		</constant>
+		<constant name="RENDERING_INFO_PIPELINE_COMPILATIONS_SPECIALIZATION" value="10" enum="RenderingInfo">
+			Number of pipeline compilations that were triggered to optimize the current scene. These compilations are done in the background and should not cause any stutters whatsoever.
+		</constant>
+		<constant name="PIPELINE_SOURCE_CANVAS" value="0" enum="PipelineSource">
+			Pipeline compilation that was triggered by the 2D canvas renderer.
+		</constant>
+		<constant name="PIPELINE_SOURCE_MESH" value="1" enum="PipelineSource">
+			Pipeline compilation that was triggered by loading a mesh.
+		</constant>
+		<constant name="PIPELINE_SOURCE_SURFACE" value="2" enum="PipelineSource">
+			Pipeline compilation that was triggered by building the surface cache before rendering the scene.
+		</constant>
+		<constant name="PIPELINE_SOURCE_DRAW" value="3" enum="PipelineSource">
+			Pipeline compilation that was triggered while drawing the scene.
+		</constant>
+		<constant name="PIPELINE_SOURCE_SPECIALIZATION" value="4" enum="PipelineSource">
+			Pipeline compilation that was triggered to optimize the current scene.
+		</constant>
+		<constant name="PIPELINE_SOURCE_MAX" value="5" enum="PipelineSource">
+			Represents the size of the [enum PipelineSource] enum.
+		</constant>
 		<constant name="FEATURE_SHADERS" value="0" enum="Features" deprecated="This constant has not been used since Godot 3.0.">
 		</constant>
 		<constant name="FEATURE_MULTITHREADED" value="1" enum="Features" deprecated="This constant has not been used since Godot 3.0.">