Turns out that after the caching changes the controllers were loading fast enough that `this.remove( this.children[ 0 ] );` in the example code was removing the controller mesh and not the targeting visualization as intended.

Noticed that there was a significant delay in controllers reappearing after jumping into and out of a system menu, which was primarily caused by re-parsing the glTF assets. This change makes it much smoother.

Also includes a few bug fixes.

Also assed it to three existing examples. Skipped paint/sculpt because they already had simple controller visualizations.

This utility makes it super simple to load controller meshes from the webxr-input-profile registry, giving users a controller visualization that matches what they're holding in their hand, with individual components animated in response to real-world input.

Frustum: .setFromMatrix() -> .setFromProjectionMatrix()

Expose the XRInputSource.gripSpace for XR controllers

Examples: .applyMatrix() -> .applyMatrix4()

Core: rename .applyMatrix() to .applyMatrix4()

WebGLAttributes: Reduce heap allocations when using WebGL2 and partial buffer updates.

GLTFExporter: Add null check for skeleton while processing skinned mesh.

PMREMGenerator: Fix viewport/scissor settings.

Docs: Use BufferGeometry in "Drawing lines" guide.

OutlinePass: Add support for skinning/morph targets.

Docs: Improve CSS in creating-a-scene guide.

Examples: Fix use of removed GeometryUtils method.

Examples: Clean up