Parquet proto writer de-nest Protobuf wrapper classes

Existing Parquet protobuf writer support preserves the structure of any Protobuf Message objects.  This works well in most cases. However, when dealing with [Protobuf wrapper messages](https://github.com/protocolbuffers/protobuf/blob/master/src/google/protobuf/wrappers.proto), users may prefer directly writing the de-nested value into the Parquet files, for ease of querying them directly (in query engine such as Hive/Presto). 

Proposal: 
- Implement a control flag, e.g., enableDenestingWrappers, to control whether or not to denest Protobuf wrapper classes. 
- When this flag is set to true, write the Protobuf wrapper classes as single primitive fields, based on the type of the wrapped **value** field.
 

|Protobuf Type|Parquet Type|
|
|-|-|-|
|BoolValue|boolean|
|
|BytesValue|binary|
|
|DoubleValue|double|
|
|FloatValue|float|
|
|Int32Value|int64 (32-bit, signed)|
|
|Int64Value|int64 (64-bit, signed)|
|
|StringValue|binary (string)|
|
|UInt32Value|int64 (32-bit, unsigned)|
|
|UInt64Value|int64 (64-bit, unsigned)|



 |

**Reporter**: [Ying Xu](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=yxu-apache)

_{**Note**: *This issue was originally created as [PARQUET-1595](https://issues.apache.org/jira/browse/PARQUET-1595). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

まず、既存の Parquet protobuf writer サポートの場所と、Protobuf Message オブジェクトを Parquet フィールドにマッピングする方法を確認します。wrapper denesting の制御フラグを定義し、その出力を一覧にある wrapper-to-primitive mappings と比較します。フラグによって、wrapper をネストされたままにするか、単一の primitive フィールドとして書き込むかを制御できれば完了です。

索引モデルが issue の本文から書いたものです。