GroupType.union() doesn't merge the original type

[asfimport]

When merging two GroupType, the union() method doesn't merge their original type which will be lost after the union.

Reporter: Abdel Hakim Deneche / @adeneche
Assignee: Abdel Hakim Deneche / @adeneche

Related issues:

• PrimitiveType.union erases original type (relates to)

_{Note: This issue was originally created as PARQUET-753. Please see the migration documentation for further details.}

[asfimport]

Abdel Hakim Deneche / @adeneche:
Openend PR#380

[asfimport]

Cheng Lian / @liancheng:
PARQUET-379 resolves the union issue related to primitive types, but doesn't handle group types.

[asfimport]

Julien Le Dem / @julienledem:
e5cd652