[C++][Gandiva] Implement Boyer-Moore string search algorithm for functions doing string matching

Discussed in https://github.com/apache/arrow/pull/5902#discussion_r351159392

**Reporter**: [Projjal Chanda](https://issues.apache.org/jira/browse/ARROW-7278) / @projjal

_{**Note**: *This issue was originally created as [ARROW-7278](https://issues.apache.org/jira/browse/ARROW-7278). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}