Schema creation from another schema will not be possible - deprecated

Imagine I have a current schema and want to create a projection schema from that. One option is the schema.Types.\*Builder but the more direct version would be to clone the schema itself without children.

`List l = new ArrayList<>();`
` for (String c : childmappings.keySet()) {`
`  Mapping m = childmappings.get(c);`
`  l.add(m.getProjectionSchema());`
` `}
` GroupType gt = new GroupType(schema.getRepetition(), schema.getName(), schema.getOriginalType(), l);`

The last line, the new GroupType(..) constructor is deprecated. We should use the version with the LogicalTypeAnnotation instead. Fine. But how do you get the LogicalTypeAnnotation  from an existing schema?

I feel you should not deprecate these methods and if, provide an extra method to create a Type column from a type column (column alone, without children. Else the projection would have all child columns).

Do you agree?

**Reporter**: [Werner Daehn](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=wdaehn) / @wernerdaehn

_{**Note**: *This issue was originally created as [PARQUET-1620](https://issues.apache.org/jira/browse/PARQUET-1620). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

まず、issue で参照されている GroupType コンストラクターのオーバーロードと、schema.Types.*Builder および LogicalTypeAnnotation の API を読みます。リンクされている移行ドキュメントと既存の projection schema の使用箇所を確認し、サポートされている方向を判断します。deprecation に関する懸念と、子を持たない schema type の作成が解決されるか、明確に文書化されれば完了です。

索引モデルが issue の本文から書いたものです。