Object3D: Add onBeforeShadow and onAfterShadow callbacks

[RenaudRohlinger]

Fixed #14921.

Reopening #25933.

This PR introduces two new optional callbacks to the Object3D class in three.js. The onBeforeShadow and onAfterShadow callbacks allow developers to execute custom code immediately before and after the shadow of a 3D object is rendered, respectively. These callbacks provide the following parameters: renderer, scene, camera, shadowCamera, geometry, depthMaterial, and group.

Example usage:

cube.onBeforeShadow = function ( renderer, scene, camera, shadowCamera, geometry, depthMaterial, group ) {

	anothercube.visible = true;
	anothercube.modelViewMatrix.multiplyMatrices( shadowCamera.matrixWorldInverse, anothercube.matrixWorld );
	renderer.renderBufferDirect( shadowCamera, null, anothercube.geometry, depthMaterial, anothercube, group );

};

cube.onAfterShadow = function ( ) {

	anothercube.visible = false;

};

Seems that we would really need it for the newly introduced BatchedMesh /cc @gkjohnson.

#14921 (comment)

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

Filesize dev	Filesize PR	Diff
668.4 kB (165.9 kB)	668.6 kB (165.9 kB)	+167 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

Filesize dev	Filesize PR	Diff
449.6 kB (108.9 kB)	449.8 kB (108.9 kB)	+167 B