Use config array instead of object for Facet Search Params

[rtloftus]

No description provided.

[demiankatz]

If you change these traits, you will also have to change all of the calls to the modified methods in the classes that use them (in this case, \VuFind\Search\Solr\Params and \VuFind\Search\Summon\Params). You should be able to use the ->toArray() method to convert objects to arrays when calling the methods for now, so we can wrap up these changes and simplify the eventual work to get rid of the remaining objects in the Params classes.

For example, change:

        $this->initFacetLimitsFromConfig($config->Results_Settings ?? null);
        $this->initFacetRestrictionsFromConfig($config->Results_Settings ?? null);

to:

        $resultsSettings = isset($config->Results_Settings) ? $config->Results_Settings->toArray() : null;
        $this->initFacetLimitsFromConfig($resultsSettings);
        $this->initFacetRestrictionsFromConfig($resultsSettings);

[demiankatz]

Thanks, @rtloftus; looks good, and tests are passing!