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.*}

Commencez par localiser la prise en charge existante de l’écriture protobuf pour Parquet et la manière dont elle mappe les objets Protobuf Message sur les champs Parquet. Définissez le flag de contrôle pour wrapper denesting et comparez sa sortie aux mappings wrapper-to-primitive listés. Le travail est terminé lorsque le flag contrôle si les wrappers restent imbriqués ou sont écrits comme des champs primitifs uniques.

Rédigé par le modèle d'indexation à partir du texte de l'issue.