CameraServiceProxy: Log camera usage metrics

- Add new events for camera usage by camera facing
- Dump stored camera events into metrics logs
- Shuffle event ordering for privacy
- Limit history to 100 entries at most

Test: Verify event log collection includes camera events
Bug: 32449509
Change-Id: I2e80b84f9bba3691893dca653ac085fef0b6c98c