Solves #3877

It enables the disableSelectedItemFiltering feature for searchable inputs by always setting the filter function's selected parameter to false.

This works for the internal defaultFilter and should work for any custom filter function that relies on the selected parameter to remove from the list.

Lastly, I added some tests to assert:

• disableSelectedItemFiltering when input is not searchable
• disableSelectedItemFiltering when input is searchable (uses defaultFilter)
• filter function's selected paramater is alwaysfalse when disableSelectedItemFiltering and searchable are enabled (generic test for any custom filter function)