Implement restricted metrics changed operation

Very generally follows the pattern of active configs/data fetch
broadcasts.

A few things are still todo:
  - tests
  - resending all pending intents on statsd restart
  - returning the current
  - code optimizations/cleanups

Test: m
Test: atest statsd_test
Bug: 268141944
Ignore-AOSP-First: U feature
Change-Id: I1f8c52c6dc0570630c92d29adb6ce8b14c08c3e7
22 files changed