UX: Autocomplete suggestions should be unselected by default (PR #11637)

When you type # or @ in the search box, a popup appears with autocomplete suggestions. Currently, when the popup is rendered it has the first item selected and upon pressing Enter, the first item is inserted into the search box. The problem with this behavior is that the first suggestion may not be what you want, and if you are typing quickly and hit enter, the first suggestion (which is not what you want) is inserted in the search box.

This PR amends the popup so that it has no suggestions selected by default which means the enter key will not insert anything unless you select a suggestion via the up or down arrow keys.

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