* feat: add MenuItem.userAccelerator property
This allows folks to read the user-assigned accelerator that macOS users can provide in system preferences. Useful for showing in-app shortcut help dialogs, you need to know if the accelerator you provided is not being used in favor of a user assigned one.
* chore: update syntax
* chore: add safety check for command index being -1
* fix: correctly handle shifted char in accelerator
* test: use actual accelerator of NSMenuItem
* chore: simplify KeyboardCodeFromStr
* chore: GetAcceleratorTextAt is testing only