Removes the playback handle from the synchronizer API and integrates it
into the device, removing the ISynchronizer interface completely.
This has been discussed in more detail in #126047 and its main purpose is to unify the handling of synchronizer events, especially seek which needed different logic for jack vs other backends.
OpenAL now needs a silence playback handle for synchronization but all
other backends are pretty straightforward just counting the mixed
samples in the SoftwareDevice with some specializations for specific
backends that had their own synchronizers before.
Note: CoreAudio changes are untested as I don't have a Mac.
Pull Request: https://projects.blender.org/blender/blender/pulls/133191
57117497fe