[Gandiva] Use non-platform specific integer types for lengths, indexes

There are many instances of using `unsigned int` and `int` for array indexes. This may cause issues on Windows

**Reporter**: [Wes McKinney](https://issues.apache.org/jira/browse/ARROW-3333) / @wesm

_{**Note**: *This issue was originally created as [ARROW-3333](https://issues.apache.org/jira/browse/ARROW-3333). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}