[KHintsSettings] Update AA_DontShowIconsInMenus at runtime

CHANGELOG: Changing the "Show icons in menus" setting will now immediately be applied to running applications

Differential Revision: https://phabricator.kde.org/D7344

Cherry-picked and corrected from plasma-integration: 2434bafcb168467f6763a20226918d27afa26744
Committed from host : Portia.local