Nodes: New features and revisions

[sunag]

Description

CacheNode

The new caching system will be the basis for radiance and irradiance flows which should use different caches, it also adds partial support for environment using Texture2D in WebGPU but needs PMREM to work properly. The cache will also be used in upcoming SwitchNode and LoopNode features.

API:

const isolatedNode = cache( someNode ); // creates an independent cache

StackNode

API:

const computeShaderNode = new ShaderNode( ( inputs, stack ) => {

	// ...

	const storageElementNode = element( someStorageNode, instanceIndex );

	// StackNode API -> stack.assign( targetNode, sourceNode )

	stack.assign( storageElementNode, valueNode );

} );

This contribution is funded by Google

[sunag]

@mrdoob @LeviPesin stack.assign( a, b ) instead of assign( a, b ).build( builder ). More simple and stable.