Add shortcut aria label for unreadable shortcuts

[talldan]

Description

Fixes #9362

Some keyboard shortcuts contain characters that screen readers don't typically read (e.g. the toggle sidebar shortcut Cmd+Shift+,). This PR adds an aria-label for those shortcuts. The changes:

• Adds a new utility function in keycodes for building an aria-label string.
• Adds a shortcut component that can receive the additional aria label prop.
• Implements the shortcut component in MenuItem and Tooltip

How has this been tested?

• Tested using voiceover

Screenshots

Types of changes

Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.

[afercia]

@talldan thanks so much for tackling this. Unrelated but since we're here: I'd suggest to take the opportunity to fix the string
Navigate to a the next part of the editor.

where the a seems a typo.

[talldan]

Thanks for catching that @afercia - added a commit to fix it.

[youknowriad]

Nice 👍