Update power_anomaly_event proto fields

- add enum PowerAnomalyType/PowerAnomalyKey
- update the func to get anomaly index

Test: manual
Bug: 291689623
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:356be9109080bc54232ff801b739ec10cab4fdfa)
Change-Id: If4e6684c8169dfa3edd4e18a11d518737a3b2840
5 files changed