Support up/down arrow keys in new dropdowns

When a dropdown has a search field, the up/down arrow keys aren't usable for item selection. It would be nice if they could be.

cc @iamphill @DouweM

Started branch 14455-support-up-down-arrow-keys-in-new-dropdowns

(Didn't mean to create that branch, was just testing the "New Branch" feature!)

Reassigned to @iamphill

mentioned in merge request !3385 (merged)

Status changed to closed by commit a1c794c5

mentioned in commit a1c794c5

Mentioned in commit pfjason/gitlab-ce@a1c794c5