[Dolphin] Hide tooltip instantly on key press

Summary:
Instantly hide tooltip shown over an element when a key is pressed.

Currently, when pressing an alphanum key to select a different file,
the tooltip continues to cover much of the window - often hiding that newly selected file from view.

Reviewers: #dolphin, ngraham, elvisangelaccio

Reviewed By: #dolphin, elvisangelaccio

Subscribers: broulik, elvisangelaccio, kfm-devel, pdabrowski

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D22512