Improve tests for Base Params and Solr Options; fix related issues.

[demiankatz]

No description provided.

[demiankatz]

@EreMaijala, this PR revises the VuFind\Search\Base\Params test to actually test the Base class instead of using Solr. Doing so required some special logic to deal with mock class names when determining the search class ID. I then added a VuFind\Search\Solr\Options test to ensure that the search class ID determination still works correctly for normal objects, which revealed a situation where a null value could get passed to a method expecting a Config object, so I addressed that as well.

I'm not exactly sure why the view initialization logic was factored to a trait when the actual properties and methods related to views are part of the base class, but I decided not to pull on that thread right now, as I already have enough distractions. Something that may benefit from a future review, though!

[EreMaijala]

@demiankatz With those fixes done, consider this approved.

[demiankatz]

Thanks, @EreMaijala -- I believe I've addressed your review comments, but I've also enabled branch protection, so now I need your formal approval to merge this. I have a lot on my plate this week, so I don't mind waiting until you get back. :-)