[C++] Document and rename is_in_meta_binary

The is_in_meta_binary and index_in_meta_binary functions do not have any "_doc" elements. I had simply ignored them assuming they were some kind of specialized function that shouldn't be exposed for general consumption (see ARROW-13949) but I recently discovered they are legitimate binary variants of their unary counterparts.

If we want to continue to expose these functions we should rename them (meta I assume means meta function but the python/r user has no idea what a meta function is) and add _doc elements.

**Reporter**: [Weston Pace](https://issues.apache.org/jira/browse/ARROW-14262) / @westonpace
#### Related issues:
- [[C++] The index_in_meta_binary/is_in_meta_binary kernels are missing a docstring](https://github.com/apache/arrow/issues/30288) (is related to)

_{**Note**: *This issue was originally created as [ARROW-14262](https://issues.apache.org/jira/browse/ARROW-14262). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}