Record controller and hands events for later playback

[matthargett]

To be able to integration test WebXR applications in commodity virtualized Linux containers, it would be useful if the emulator could record/save and load/playback a series of controller, hands, and plane detection events.

Being able to get this quality feedback before going to expensive on-device testing is key for scaling engineering efforts in an economically defensible way.

FWIW, we took this same approach on a game console project I worked on where we used react-native-web and injected some extra gamepad extensions, so we could get app startup profiling data and basic integration smoke test feedback before running a fuller test suite on rare prototype hardware.