ParquetMetadataConverter.java is too long

[asfimport]

ParquetMetadataConverter is huge and could benefit from splitting into a few smaller classes with well defined responsibilities.

Reporter: Alex Levenson / @isnotinvain
Assignee: Ashish Singh / @SinghAsDev

_{Note: This issue was originally created as PARQUET-310. Please see the migration documentation for further details.}

[asfimport]

Ryan Blue / @rdblue:
We should define its public API at the same time and make sure the packages line up.