Allow Ctrl+Q Shortcut to Close

[sonic2kk]

Added the ability to use Ctrl+Q to quit the application, which is common on Windows and Linux to close programs. These changes were tested on Arch Linux using JetBrains Rider.

I am open to feedback on implementation, but based on how shortcuts are currently wired, I think I did this in a way that fits the current codebase.

I have worked with Qt in the past, and there is a concept of KeySequences that have built-in shortcuts for some actions. AvalonUI seems to have something similar, but many examples seem to use XML (https://docs.avaloniaui.net/docs/concepts/input/binding-key-and-mouse). I am not familiar enough with the technology here to know if this is relevant to this project. 😅

This is my first experience contributing to a C# codebase. I tried to follow the existing patterns that were in place. Let me know if I missed anything. Thanks!

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EDIT: This would "work" on macOS, but on that platform, Cmd+Q is more commonly used. As there appears to be ongoing work to support macOS, I can add relevant support to check the correct modifier for macOS, but may need some guidance on how to check the current platform.

[thesupersonic16]

On Windows Ctrl + Q doesn't seem common, almost all software I use does not respond to it or does not treat it as quitting.
On macOS, I believe ⌘ is bound to the Meta key. I do not own an OSX machine to test that.
On my KDE Linux machine it seems to work on most software I have.

For now I think this is fine, though there is a good chance the code will get replaced later on when the macOS PR is ready.