Tree shaking improvements

[mrxz]

This PR improves the tree-shakability of Spark by focussing on classes that users might not need or use. See #321

• Ensures the SplatSkinning class is only included when used, including its shader chunks.
• Ensures SplatEdit and SplatEditSdf are tree-shaken, unless imported.
  • This is done by adopting the three.js approach of having isType = true properties on the classes for type discrimination. Since these can't easily be used in TypeScript, however, helper type guard functions are introduced (isSplatEdit and isSplatEditSdf).
  • NOTE: The SplatEdits class is still included at all times as SplatMesh is capable of constructing this: SplatMesh.ts#975
• Ensures SparkXr and related code is tree-shaken.
  • There was a lot of duplication between SparkXr.ts and hands.ts, but now the former imports from the latter
  • Annoyingly a simple .length prevented tree-shaking, so resorted to a reduce function which can be statically analyzed for elimination (alternatively an IIFE could be used for this as well)

[asundqui]

Curious about these changes? Do they match another part of the code or a previous source? I forget but I think I may have edited them from the original data I used. Don't feel strongly either way but just curious!

[mrxz]

There were two almost identical lists, one in hands.ts and one in SparkXr.ts, the latter seemed more recent so those values are now used. They seemed close enough that either one would probably be fine.

One alternative could be to retrieve the joint radii from the WebXR API (https://www.w3.org/TR/webxr-hand-input-1/#dom-xrframe-filljointradii), as that could in theory align better with the user's actual hands (bar spec mandated anonymization)

[asundqui]

This is great, anything that reduces bundle size and opts-in code sounds good to me! @oscarlorentzon @dmarcos we should merge this yes?

[oscarlorentzon]

JointEnum is exported from index.ts, so this seems to break compatibility for anyone currently using let j: JointEnum. Do we need handle that for minor version releases?

[mrxz]

Frankly I doubt people use the JointEnum type, as it's effectively just the WebXR Hand Input Module joint names. The interaction with the WebXR API is handled by the SparkXr/hands.ts code and from the user's code everything is keyed on JointId.

Mentioning the change in the release notes should suffice IMHO.

[oscarlorentzon]

This is great, anything that reduces bundle size and opts-in code sounds good to me! @oscarlorentzon @dmarcos we should merge this yes?

Looks good. It would be good to clarify the potential API compatibility issue before we merge.