Update CarServiceHelperService to use unstable AIDL

android.automotive.watchdog.internal is being made unstable to simplify
adding new changes. Update CarServiceHelperService to use the unstable
version of this AIDL.

Test: m + presubmit
Flag: EXEMPT refactor
Bug: 379899449
Change-Id: I41c2ed364193be2b07f517dac30b0fab4ce94764