Summary:
Otherwise there's no visual feedback that you can just hit
Return.

This requires refactoring the item list code slightly not to
implicitly focus the list when the current index changes (so
focus isn't moved away from the search field). Instead it's
now done on mouse over and manually by external callers after
they set an index.

Reviewers: #plasma, mart

Reviewed By: #plasma, mart

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D9962