trigger modifier-only shortcuts when any modifier is released

Previously multi-modifier modifier-only shortcuts are triggered when all relevant keys are released within a certain time limit. This is inconvenient when users want to trigger such a shortcut repeated, for example when switching keyboard layouts. In addition, the time limit imposes accessibility difficulties.

Instead, trigger such shortcuts when any modifier is released.

cc @odeda

@teams/usability for UX review. Not sure if the recording functionality in kguiaddons should be modified accordingly. Currently for recording the user needs to release all pressed modifiers within a time frame.

Also not sure if this should target 6.1.x or 6.2.