WayVR: IPC & Dashboard integration support

[olekolek1000]

wlx:
- Use numeric constants for overlay z-orders instead of magic values

WayVR:
- Implement WayVR IPC Server (threadless)
- Implement WayVR IPC Client (https://github.com/olekolek1000/wayvr-ipc)
- Dashboard integration support
- New `ToggleDashboard` input action available
- Update wayvr.yaml config with how-to instructions for the dashboard
- Refactoring and minor improvements

WayVR IPC:
- Add client methods: `WvrDisplayCreate`, `WvrDisplayGet`, `WvrDisplayList`, `WvrProcessLaunch`, `WvrProcessList`, `WvrProcessTerminate`

Dashboard integration instructions: https://github.com/galister/wlx-overlay-s/blob/160979ebe4f1609bac9c9fe9d6de4cb7c3d34c00/src/res/wayvr.yaml

[galister]

nice, thanks!