Update media3 button tests and error handling

- Use a fake Media3ActionFactory in kosmos
- Wrap media3 handler calls in a try-finally, to ensure that the
  controller disconnects
- Minor edits from code review

Flag: com.android.systemui.media_controls_button_media3
Bug: 360196209
Test: atest Media3ActionFactoryTest MediaDataLoaderTest
Change-Id: Ic91401af5b030da5bfa4ff188d1b55b69b72be5f