Add linter to restrict direct usage of registerContentObserver() API.

Forbid direct usage of register/unregister content observer APIs from the ContentResolver class.
Instead direct the caller to use wrapper APIs in SettingsProxy and its sub-classes.

Bug: 353191254
Test: atest RegisterContentObserverViaContentResolverDetectorTest
Flag: NONE new linter check

Change-Id: I50db306d5dc7c2ac6a146586f7d336c32765b462
4 files changed