Replace FileMetadata in parquet writer with in memory representation.

[liurenjie1024]

Currently in parquet writer the FileMetadata we used is this one, which is auto generated from parquet thrift definition. We should use this one for in memory operations.

[jonathanc-n]

@liurenjie1024 I think the current problem with this is that ArrowFileReader (reader) returns ParquetMetadata and AsyncFileWriter (writer) returns the thrift definition. The solution I was thinking of is creating a conversion from thrift -> ParquetMetadata, but this seems like an unnecessary step. I think keeping both functions so that the parquet writer can convert to datafile given any of the two metadatas without an unnecessary conversion step in between seems to be fine.