Added the ability to run and combine multiple animations simultaneously

[mohammadbaghaei]

Added the ability to run and combine multiple animations simultaneously with appendAnimation and detachAnimation methods, updated documentation, upgrade to three.js r171 and update all dependencies to latest version

[elalish]

Wow, this is quite a feature, thank you! To make this easier to review and merge, would you be so kind as to split the dependency updates into a separate PR from the animation work? We should be able to quickly merge the updates, but we'll probably need some back-and-forth on the API change. Honestly, it's looking really good though!

[mohammadbaghaei]

Hey there! Here's my rework of that PR message:

👋 Thank you for the helpful feedback! I've made the following changes in this PR:

• Fixed all the mentioned issues
• Enhanced modelviewer.dev styles for better presentation, especially in the examples section
• Updated dependencies in a separate commit
• Improved appendAnimation and detachAnimation methods to automatically handle invalid parameters
• Added automatic parameter type conversion - numbers and booleans can now be passed as strings (case-insensitive)
• For better AR support across different devices (ref: issue AR/MR mode doesn't work on PICO headsets / Make Hit Test API optional #4960), moved hit-test to optionalFeatures

Let me know if any further adjustments are needed! 🙂

[elalish]

Thanks! As this is my last day (see #4975), I'm going to pass this on to one our other maintainers, @diegoteran, who I already talked to about this PR. Looks like a promising feature!