Clean up PbapClientServiceTest

This change:
- Reorganizes the test class by what's being tested so it's easier
  to follow along and see what's covered.
- Removes the BluetoothMethodProxy hack by using a MockContentResolver
  and MockContentProvider
- Changes a few test names to accurately reflect what they do now that
  there's not broadcast receiver for ACL state changes

Flag: EXEMPT, test only change
Bug: 365626536
Test: atest com.android.bluetooth.pbapclient
Change-Id: I5a954df17f0d54ea3cab24da9a6b3a857fcc2f64