feat: parse Parquet schema from ParquetMetadataConverter

[devinrsmith]

This removes the DH's duplication of schema reading logic, and removes the warning

DO NOT RELY ON {@link ParquetMetadataConverter} FOR THIS! USE

There has been no tests to indicate that using ParquetMetadataConverter causes any issues. It may have been true historically, but does not seem to be true anymore.

[devinrsmith]

This is a much smaller piece of #6189.

At least, we need to figure out if there is any merit to

DO NOT RELY ON {@link ParquetMetadataConverter} FOR THIS! USE {@link ParquetFileReader}

[malhotrashivam]

I have verified that all the recent bug fixes and changes we have done in Parquet type deduction logic is included in the ParquetMetadataConverter, so this change looks good to me, other than a small minor comment.