Cell Level Encryption

Cell level encryption can do finer-grained encryption than modular encryption(Parquet-1178) or file encryption. The idea is only some fields inside the column are encrypted based on a filter expression. For example, a table with column a, b, c.x, c.y, d, we can encrypt column a, c.x where d == 5 and c.y > 0.

**Reporter**: [Xinli Shang](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=shangx@uber.com) / @shangxinli
**Assignee**: [Xinli Shang](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=shangx@uber.com) / @shangxinli
#### Externally tracked issue: [https://docs.google.com/document/d/1PUonl9i_fVlRhUmqEmWBQJ8zesX7mlvnu3ubemT11rk/edit#heading=h.kkuoyw5u0ywe](https://docs.google.com/document/d/1PUonl9i_fVlRhUmqEmWBQJ8zesX7mlvnu3ubemT11rk/edit#heading=h.kkuoyw5u0ywe)

_{**Note**: *This issue was originally created as [PARQUET-2116](https://issues.apache.org/jira/browse/PARQUET-2116). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

Start with the externally tracked Google design document and the PARQUET-1178 context referenced in the issue. Define the implementation scope and acceptance criteria for encrypting selected fields, including nested fields, according to filter expressions; the issue provides no repository files or tests to run.

Written by the indexing model from the issue text.