Add union API to BloomFilter interface

Sometimes, one may want to build a file-level bloom filter by union all row groups bloom filters so that to save some memory. Add a union API that could make it easy to use.

**Reporter**: [Junjie Chen](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=junjie) / @chenjunjiedada
**Assignee**: [Walid Gara](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=garawalid) / @garawalid
#### PRs and other links:
- [GitHub Pull Request #768](https://github.com/apache/parquet-mr/pull/768)
- [GitHub Pull Request #770](https://github.com/apache/parquet-mr/pull/770)

_{**Note**: *This issue was originally created as [PARQUET-1815](https://issues.apache.org/jira/browse/PARQUET-1815). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

Inizia con l’interfaccia BloomFilter e rivedi le GitHub Pull Requests #768 e #770, collegate dall’issue. Confronta la loro API di unione proposta e determina il comportamento previsto per combinare i filtri Bloom dei gruppi di righe; il lavoro è completo quando l’interfaccia offre un modo semplice per creare un filtro a livello di file.

Scritto dal modello di indicizzazione a partire dal testo della issue.