[C++] AsofJoinNode 128-bit hashing

A recent version of `AsofJoinNode` uses 64-bit hashing for by-key values. This [leads to a non-negligible probability of collisions](https://github.com/apache/arrow/pull/13880) that are not arbitrated. Using 128-bit hashing, the probability will become negligible.

**Reporter**: [Yaron Gvili](https://issues.apache.org/jira/browse/ARROW-17653) / @rtpsw

_{**Note**: *This issue was originally created as [ARROW-17653](https://issues.apache.org/jira/browse/ARROW-17653). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

Start by locating AsofJoinNode and tracing how it hashes by-key values during as-of joins. Compare the current hashing path with the collision concern described in the issue; done means the node uses 128-bit hashing for these values and the relevant behavior is covered by the project’s existing validation or tests.

Written by the indexing model from the issue text.