Enable exact search for maven registry provider

[andre2007]

This will enable downloading dub packages on dub run as introduced by Seb (#1428) also for maven repository provider.

Only exact search is possible, which is sufficient for dub run.
For a "real" search different html dialects (Nexus, Artifactory, ...) has to be parsed.
For example the html code of this site has to be parsed to get the 3 artifacts
https://repo1.maven.org/maven2/com/devspan/vendor/jquery/

[dlang-bot]

Thanks for your pull request and interest in making D better, @andre2007! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
Please verify that your PR follows this checklist:

• My PR is fully covered with tests (you can see the coverage diff by visiting the details link of the codecov check)
• My PR is as minimal as possible (smaller, focused PRs are easier to review than big ones)
• I have provided a detailed rationale explaining my changes
• New or modified functions have Ddoc comments (with Params: and Returns:)

Please see CONTRIBUTING.md for more information.

---

If you have addressed all reviews or aren't sure how to proceed, don't hesitate to ping us with a simple comment.