[C++] Support equality comparison between COO and CSX sparse tensors in SparseTensorEquals

Currently SparseTensorEquals always returns false when it gets COO and CSX sparse tensors.

It should support comparing the items in the sparse tensors.

**Reporter**: [Kenta Murata](https://issues.apache.org/jira/browse/ARROW-4222) / @mrkn
**Watchers**: [Rok Mihevc](https://issues.apache.org/jira/browse/ARROW-4222) / @rok

_{**Note**: *This issue was originally created as [ARROW-4222](https://issues.apache.org/jira/browse/ARROW-4222). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}