Migrate Tethering#dump to use runWithScissorsForDump

This change includes:
  1. Refactor the logic in Tethering#dump into utils class.
  2. Move the utils class to a common place which could be referenced
     from other sub-modules.
  3. Add @MonitorThreadLeak annotation to enforce
     there is no thread leak problem.

Test: atest FrameworksNetTests NetworkStaticLibTests
Test: atest ConnectivityCoverageTests:com.android.networkstack.tethering.TetheringTest#testDumpTetheringLog
Test: adb shell dumpsys tethering (with hardcoded exception)
Fix: 312669345

Change-Id: Ia6fdfeeec2110afa0ec9e056e9db3843748845c3