Update models, add ability to spawn brush tip separately

[msub2]

This PR:

• Adds two new glTF models for the Vive Controller and separate brush tip object
• Allows the brush tip to be spawned separately and appended to an existing controller model
• Creates a new brush-tip component to allow for easier future support of additional controller models
• Adjusts some logic in getPointerPosition to better reflect the new Quest 2 controllers.

[dmarcos]

Great effort! Thanks so so much! 🏅