Clear inputs when dropdown items have been selected

Issue

From #233283 (closed):

I never noticed this- we do don't clear the data for any of the multi-select sidebar dropdowns. So if I click on Edit reviewer and type annabel, then click on myself, close the dropdown, reopen it, I'll still see annabel in the text field. Same goes for labels, assignees, etc 🤔

Proposal

Ensure that subsequent searches remove the text in the search field from the prior search.