Implement DumpSys for MediaRouter2ServiceImpl

Implemented basic version of dumpsys:
- Entry point is MediaRouterService#dump
- Added dump to: MediaRouter2ServiceImpl, UserRecord, RouterRecord,
  ManagerRecord, SessionCreationRequest, UserHandler

Bug: b/243116883
Test: adb shell dumpsys media_router
Change-Id: I7e3c148de4bdbdc72a513a8a761198f7b3e99d32