Take active screen in account and remove shortcut requirement for activating launcher

With the information about the active screen we can make an educated guess about where the attention of the user is and where they could expect the launcher to open. If on the screen no launcher could be activated, look at all launchers. Also remove the requirement for launchers to have a shortcut. This is needed to make this feature work reliably and should reduce the instances of "Meta key stopped working" happening in general. CCBUG:447962 BUG:391322 BUG:444343 BUG:437979