Widget App Handler

[HexaField]

Summary

This PR includes a basic widget abstraction has been implemented to containerize and wrap our various XRUI panels & systems. This allows us to handle the like code between all these panels (such as 3d positioning, enable/disable, show/hide etc) and all potential common future functionality (such as moving & minimising/maximising panels, wrapping in stylised containers like the oculus quest browser does) and allows for easy registration and unregistration of widgets.

• create a widget registry on the World object
• can register and unregister widgets
• can open and close widgets, they are rendered as separate XRUI panels

Future work includes renaming various functions & files. This will be done in a follow up PR to avoid collisions with #6443

References

closes #6364

Checklist

• If this PR is still a WIP, convert to a draft
• ensure all checks pass
• When this PR is ready, mark it as "Ready for review"
• Changes have been manually QA'd
• Changes reviewed by at least 2 approved reviewer

QA Steps

List any additional steps required to QA the changes of this PR, as well as any supplemental images or videos.