Clear inputs when dropdown items have been selected
#### Issue
From https://gitlab.com/gitlab-org/gitlab/-/issues/233283:
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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 :thinking:
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#### Proposal
Ensure that subsequent searches remove the text in the search field from the prior search.
issue