[Python] Allow to create field reference to nested fields that use indices

As a follow-up to ARROW-11259 we should implement referencing nested fields that use indices (eg when creating a filter expression) once ARROW-15658 is closed.

**Reporter**: [Alenka Frim](https://issues.apache.org/jira/browse/ARROW-16180) / @AlenkaF
#### Related issues:
- [[C++] Parquet pushdown filtering fails if the filter expression uses numeric field references](https://github.com/apache/arrow/issues/20114) (is blocked by)

_{**Note**: *This issue was originally created as [ARROW-16180](https://issues.apache.org/jira/browse/ARROW-16180). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}