[MINDEXER-206] Search Backend SMO and RR handle different Artifact.extension

**[Tamas Cservenak](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=cstamas)** opened **[MINDEXER-206](https://issues.apache.org/jira/browse/MINDEXER-206?redirect=false)** and commented

The two backends should not force caller to construct Query differently, but handle their own implementation specifics silently.

---
No further details from [MINDEXER-206](https://issues.apache.org/jira/browse/MINDEXER-206?redirect=false)

Start by comparing the SMO and RR search backend implementations, focusing on how each handles Artifact.extension and constructs or interprets Query. Confirm the expected behavior from the MINDEXER-206 description; done means callers can use the same Query shape while each backend handles its extension differences internally.

Written by the indexing model from the issue text.