microgesture support

The Quest Browser 38.1 support hand microgestures. They follow the OpenXR specification https://registry.khronos.org/OpenXR/specs/1.1/html/xrspec.html#XR_META_hand_tracking_microgestures and there is a demo page at https://micro-gestures-demo.glitch.me/ and the result show up in the GamePad API https://immersive-web.github.io/webxr-samples/controller-state.html

It could be interesting, assuming that others, e.g. Apple for the VisionPro or Google for AndroidXR do follow OpenXR specs for WebXR, to bring this to a similar level than hand-tracking-controls namely extending events beyond pinchstarted, pinchended and pinchmoved with, possibly (following OpenXR naming) tap (or maybe thumb_tap), thumb_location (that I initially forgot, as I somehow didn't manage to test it) and swipe_left, swipe_right, swipe_forward, and swipe_backward new events for example.

Start by reading the existing hand-tracking-controls implementation, then compare its current events with the OpenXR hand-tracking microgestures specification and the linked demo and GamePad API sample. Done means agreeing on supported gesture names and behavior, extending the controls consistently, and covering the new events across the relevant browser implementations.