OpenXR: Support a wider array of interaction profiles and inputs

[msub2]

Currently the OpenXR backend only supports a base set of inputs (pose, select, squeeze, hand input) and only two interaction profiles (microsoft motion controller and khr simple controller). While this is technically enough to implement support for the WebXR Gamepads Module in Servo, it should probably be expanded to include:

• Thumbsticks/touchpads
• Primary/secondary buttons (A/X, B/Y)
• (Optionally) A trusted button for system interactions (either /input/menu or /input/system if available).
  • This isn't necessarily required for the WebXR Gamepads Module but it would be useful to have for potential future work on navigation/permission prompts while in an immersive session.

For interaction profiles I think covering a subset of the most-used headsets would be a good start (Meta/HTC/Pico/WMR), though it shouldn't be too hard to add more if necessary. The input profile name array will also need to be set properly, as it currently just returns "generic-hand" no matter what.

[msub2]

PR for interaction profiles at #229, this is probably the one change that won't require a concurrent update in Servo as well.

[msub2]

Passing data for buttons and axes will require some more significant changes to the API. Spots that will need changing:

• mod.rs: Updating begin_animation_frame to pass along button/axes state
• event.rs: Will likely need a new event to signal that gamepad input needs to be updated. Should probably cache input state to make sure the event only fires when input has actually changed
• input.rs: Will need to update the logic in get_bindings to iterate through all the mappings present in the interaction profiles. Need to figure out how the data will be stored.

[msub2]

With WebXR Gamepads Module support done, the last major item I'd consider part of this would be hand interaction profiles (trusted/system buttons can be revisited if/when they become necessary). I'll be doing some work to get Servo's WebXR Hand Input implementation up to date, after which interaction profiles for hand tracking can then be added without much extra effort.

[msub2]

Hmm, looks like there's a little more to be done here before hand input will work. From what I can tell it looks like the Hand object is never getting created because it's trying to get state from OpenXR actions that don't exist. I'll probably need to create some new hand-specific interaction profiles

[msub2]

Closing this now that PR for hand input update is pending and #236 has merged