Improved logging and dump() on LocalTransport.

- Implemented LocalTransportService.dump()
- Implemented some missing toString() methods
- Added some extra logging statements

You can check it by running the following command in one terminal: some examples on how to use it:

$ watch -n 1 '(adb shell dumpsys activity service com.android.localtransport/.LocalTransportService | tee -a ~/tmp/dumpsys.log)'

Then in another:

$ adb shell 'settings put secure backup_local_transport_parameters "log_agent_results=true"'
$ adb shell bmgr backupnow android
$ adb shell bmgr run

Test: m -j LocalTransport && adb install $OUT/system/priv-app/LocalTransport/LocalTransport.apk # then commands above
Bug: 394173116
Flag: EXEMPT changes on debugging components only

Change-Id: I11d239f9b2a70de8f94ff7f9f6df0be79fc69d36