[Data] Move BlockWritePathProvider to separate file

[bveeramani]

Why are these changes needed?

1. BlockWritePathProvider won't be related to FileBasedDatasource after [Data] Add Datasink #40199
2. BlockWritePathProvider is deprecated by [Data] Deprecate BlockWritePathProvider in favor of FilenameProvider #40297. Moving it out of file_based_datasource makes our code more readable.

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[scottjlee]

LGTM, assuming tests pass after merging in latest master.