This is a proof of concept for cleanup we should do for all of
our DataSource implementations as we move toward stabilizing
parts of the API.
- Move all XDataSourceFactory classes to be inner classes.
- Remove chained constructors for XDataSourceFactory classes. Keep
required args going through constructors. Use setters for the
rest.
- Not applicable in this case, but we probably want to deprecate
all but the no-arg method for instantiating eac XDataSource
instance (with the all-arg method kept but with the intention
of making it package private).
PiperOrigin-RevId: 274162076
