Add `TempoSyncBarModelEditor` which adds a tempo sync option to a `BarModelEditor`. Please note that the code was mostly copied and adjusted from the `TempoSyncKnob` class. It was not attempted yet to unify some of the code because with the current design it seems to be a road to "inheritance hell". A better solution might be to refactor the code so that it is more composable.
Another option might be to move the tempo sync functionality into a class like `FloatModelEditorBase`. Although this would not be a 100% right place either because `TempoSyncKnobModel` inherits from `FloatModel`. In that case we'd have specialized code in a generic base class.
Adjust `LadspaWidgetFactory` so that it now returns an instance of a `TempoSyncBarModelEditor` instead of a `TempoSyncKnob`.
Remove the extra layout code from `LadspaMatrixControlDialog.cpp` as most things are bar editors now.
Adjust `TempoSyncKnobModel` so we do not have to make `TempoSyncBarModelEditor` a friend of it.
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