allow form elements to override Chosen library options

Overrides the default no_ results_text and search_contains placeholder options via the chosen_selectfield widget. It would be easy to add more option overrides, but maybe the form would get too big?

The last submitted patch, 3: override_default_chosen_options-3431221.patch, failed testing. View results →
- codesniffer_fixes.patch Interdiff of automated coding standards fixes only.

I have created a new MR with the changes from #3431221-3: allow form elements to override Chosen library options → but for 4.0.x-dev version.
No further changes exist in my code.

PS: It seems that the tests are failing but I am not sure if they break due to this code or if they were already broken from the past; in the later case we should handle them in a different issue.

I think they fail only cause of missing schema.