Allow overriding system-reserved shortcuts

[tofumatt]

Fix #33.

Updated version of #125 with the linting errors fixed, and "OK" as the default option in the dialog.

Works as-expected in my app:

https://github.com/sindresorhus/KeyboardShortcuts/assets/90871/d155611d-d1b2-4209-97b0-490cd326a1b0

[sindresorhus]

What keyboard combination do you use to test the dialog (to trigger it)?

[tofumatt]

I used "Command + Escape", which is actually my usual keyboard shortcut for an app I'm transitioning to use KeyboardShortcuts from another library, so at first was very confused why it wouldn't work (the old library never detected it was a "reserved shortcut") 😅