PARQUET-346: Minor fixes for PARQUET-350, PARQUET-348, PARQUET-346, PARQUET-345

[isnotinvain]

PARQUET-346:
ThriftSchemaConverter throws for unknown struct or union type
This is triggered when passing a StructType that comes from old file metadata

PARQUET-350:
ThriftRecordConverter throws NPE for unrecognized enum values
This is just some better error reporting.

PARQUET-348:
shouldIgnoreStatistics too noisy
This is just a case of way over logging something, to the point that it make the logs unreadable

PARQUET-345
ThriftMetaData toString() should not try to load class reflectively
This is a case where the error reporting itself crashes, which results in the real error message getting lost

[isnotinvain]

FYI, as far as I can tell, this implementation is faster than:

try {
  final int id = enumLookup.get(value);
} catch (NullPointerException e) {
  throw new ParquetDecodingException(...)
}

I thought maybe the above would be better because there's sort of a hint to the branch predictor that the 'normal' case is for this not to throw so predict that... but i did a small benchmark and the if statement seems to be faster

[tsdeng]

Maybe add a comment to state the struct being passed in should be file schema stored in json, and the isUnion method will nor be called...
Basically just document why it's separated from the normal convert code path in case we forget it in the future

[tsdeng]

Minor commet, LGTM

[isnotinvain]

@tsdeng updated with comments, and cleaned up usage of ThriftSchemaConverter

[tsdeng]

+1

[isnotinvain]

Thanks!