plugins/zoom, plugin/magnifier: Add missing "Zoom In" keyboard shortcuts
"Zoom" effect initially sets "Meta+KeyPlus" as the the main shortcut for "Zoom In" action and "Meta+KeyEqual" as alternative.
However only "Meta+KeyPlus" is registered as the default shortcut. That makes harder for user to restore appropriate defaults.
This commit registers "Meta+KeyEqual" as an "Global Alternate" shortcut
"Magnifier" is an alternative to "Zoom" effect. They use the same keyboard shortcuts for similar actions.
However, 2 keyboard shortcuts ("Meta+KeyPlus" and "Meta+KeyEqual") are registered for "Zoom" by default, while for "Magnifier" there is only one ("Meta+KeyEqual").