Create searchable single select component

[rsadres]

Several teams have use for a component that functions like SearchableMultiSelect but allows only one selection. Since there have been multiple requests for this, let's make a new component or a variant of SearchableMultiSelect.

Users search, click on their selection, and the search field turns into a Selection - users can remove the selection to start the process again

prototype - https://appnexus.invisionapp.com/share/5UQSGPSVPXR#/349838004_SearchableSingleSelect_Copy_4