fix: Zoom-in/out using keyboard shortcut not working correctly

[Oliver-Loeffler]

Zoom-In/Out was supposed to work with keyboard shortcuts. For Zoom-In MODIFIER++ and for Zoom-Out MODIFIER+/ were defined. The predefined KeyCombinations were not working, there seems something wrong with how KeyCodes are handled especially on macOS but also on Windows. This might become an issue for OpenJFX which is a separate thing.

I've played a while with suitable settings which work on Win/Mac/Linux and settled with following idea:

Platform(s)	Accelerator	Action	Preview	App (with GER keyb. layout)
WIndows, Linux	CTRL++	Zoom In		ok
WIndows, Linux	CTRL+-	Zoom Out		ok
WIndows, Linux	CTRL++ (on num key pad)	Zoom In		ok
WIndows, Linux	CTRL+- (on num key pad)	Zoom Out		ok
macOS 12.0.1	CMD++	Zoom In		ok
macOS 12.0.1	CMD+-	Zoom Out		ok
macOS 12.0.1	CMD++ (on num key pad)	Zoom In		ok
macOS 12.0.1	CMD+- (on num key pad)	Zoom Out		ok

Platform(s)	Accelerator	Action	Preview	App (any keyb. layout with cursors)
WIndows, Linux	SHIFT+CTRL+up	Zoom In		ok
WIndows, Linux	SHIFT+CTRL+right	Zoom In		ok
WIndows, Linux	SHIFT+CTRL+left	Zoom Out		ok
WIndows, Linux	SHIFT+CTRL+down	Zoom Out		ok
macOS 12.0.1	SHIFT+CMD+up	Zoom In		ok
macOS 12.0.1	SHIFT+CMD+right	Zoom In		ok
macOS 12.0.1	SHIFT+CMD+left	Zoom Out		ok
macOS 12.0.1	SHIFT+CMD+down	Zoom Out		ok

The DocumentWindowController offers a mainKeyEventFilter where those double accelerators can be tracked. All key handling happens in MenuBarController but this is called from mainKeyEventFilter in DocumentWindowController.

Issue

Fixes #424

Progress

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