[Java] Inconsistent logic for type IDs in Union vectors

The current logic for calculating the type IDs in UnionVector#getField and DenseUnionVector#getField is:
1. DenseUnionVector uses an increasing counter 
1. UnionVector uses the ordinal of the type enum
1. Both completely ignore the type IDs provided at construction as part of fieldType (if provided)

We encountered this inconsistency while testing a direct roundtrip of a union vector between pyarrow and Java with the C Data Interface ('direct' here means without using VectorSchemaRoot/RecordBatch). The identifiers for the type IDs differ after completing a roundtrip. 

 

**Reporter**: [Roee Shlomo](https://issues.apache.org/jira/browse/ARROW-14271) / @roee88

_{**Note**: *This issue was originally created as [ARROW-14271](https://issues.apache.org/jira/browse/ARROW-14271). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

Comece com UnionVector#getField e DenseUnionVector#getField e, em seguida, rastreie como fieldType e seus IDs de tipo fornecidos são tratados durante a construção. Reproduza o roundtrip direto de pyarrow para Java por meio da C Data Interface e verifique se ambos os tipos de vetor preservam IDs de tipo consistentes após o roundtrip.

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