Turn around the inheritance dependency for MediaOutputAdapter classes.

- Rename `MediaOutputAdapter` to `MediaOutputAdapterBase`.
- Rename `MediaOutputBaseAdapter` to `MediaOutputAdapterLegacy`.
- Make `MediaOutputAdapterLegacy` a child of `MediaOutputAdapterBase`.

Flag: EXEMPT refactor
Bug: 387570618
Fix: 387570618
Test: atest SystemUiRoboTests:MediaOutputAdapterLegacyTest
Change-Id: Ic8ef1856ad2fd27252918fbb7f113079399dcd11