Minor Description
Add a static convenience method ModifiableSolrParams#of(SolrParams) which returns the same instance if it already is modifiable, otherwise creates a new ModifiableSolrParams instance.
Rationale: when writing custom SearchComponents, we find that we often need to ensure that the SolrParams are modifiable. The copy constructor of ModifiableSolrParams always creates a copy, even if the SolrParms already are modifiable.
Alternatives: The method could also be added as a convenience method in SolrParams itself, which already has static helper methods for wrapDefaults and wrapAppended.