p5.xr Enter VR button, controller functionality, interface primitives, and basic locomotion

In this proposal, I outline the addition of key features to p5.xr, in order to expand the VR capabilities of p5.js. This includes an improved Enter VR button for WebXR integration, controller APIs that expose orientation and provide an out-of-the-box controller representation, menu interface primitives including buttons and raycast pointers, and the beginnings of a locomotion system to allow a user to traverse a scene. Throughout each phrase of this project, I will add documentation and examples. I intend to help validate XR features across Oculus and Valve Index devices.