Nodes: Introduce Node.needsUpdate=true

[sunag]

Related issue: Closes #27895

Description

In the vast majority of cases, cacheKeys are being generated without any real need, which would be to change the TSL code, causing overloading. This PR introduces node.needsUpdate=true so that the system can identify when it is really necessary to recreate the Node's cacheKey.

Comparation

Comparison below of webgpu_backdrop_water in the range of 1 to 4 seconds.

Before	Now

When should I use it?

Every time you need to update a specific Node chain, for exemple:

// mix( a, b, c ) = mix( aNode, bNode, cNode )
material.colorNode = mix( color( 0x0487e2 ), color( 0x0066ff ), normalWorld.y );

// ... in the software cycle

material.colorNode.aNode = color( 0xffffff );
material.colorNode.needsUpdate = true;

[RenaudRohlinger]

This solution is so good!! 🙏

[mrdoob]

this.version and this._version?

[RenaudRohlinger]

In the WebGLRenderer the strategy was often this.version !== thisProperties.__version.

Would rename this._version to this.__version be better? Where this.__version is basically this.cachedVersion.
/cc @mrdoob

[mrdoob]

Ah right yes.
Forgot about the internal usage...

Looking good then! Let's follow how we did it in WebGLRenderer. I've never seen anyone having issues with it.