Wifi Usability Metrics Proto Update

Generate WifiIsUnusableEvent when there is a data stall or a firmware
alert. In WifiIsUnusableEvent, store metrics related to time, packet
counts, trigger reason, and score.

Also, log ExperimentValues that we plan to change through global
settings varaible.

This logging is enabled by setting WIFI_IS_UNUSABLE_EVENT_METRICS_ENABLED
to 1. By default, this metric is not collected.

Manual Check Process:
- Connect to a network
- adb shell settings put global wifi_is_unusable_event_metrics_enabled 1
- adb shell dumpsys wifi wifiMetricsProto
- Move away from the ap to trigger data stall
- adb shell dumpsys wifi | grep -10 WifiIsUnusableEventList
- Verify that there is a WifiIsUnusableEvent

Bug: 77603216
Test: Unittest (settings core/tests/coretests).
Test: Manual Check.
Change-Id: I2d8425a420f5ba18e3eee0e11b6f35f6239a97b2