PARQUET-139: Avoid reading footers when using task-side metadata

This updates the InternalParquetRecordReader to initialize the ReadContext in each task rather than once for an entire job. There are two reasons for this change:

1. For correctness, the requested projection schema must be validated against each file schema, not once using the merged schema.
2. To avoid reading file footers on the client side, which is a performance bottleneck.

Because the read context is reinitialized in every task, it is no longer necessary to pass the its contents to each task in ParquetInputSplit. The fields and accessors have been removed.

This also adds a new InputFormat, ParquetFileInputFormat that uses FileSplits instead of ParquetSplits. It goes through the normal ParquetRecordReader and creates a ParquetSplit on the task side. This is to avoid accidental behavior changes in ParquetInputFormat.
Why has the type parameter T been dropped here?