Resolve "Keyboard shortcuts modal is broken"

What does this MR do?

Updates the keyboard shortcuts modal to use <kbd> elements and pull in all the relevant styles for them.

Are there points in the code the reviewer needs to double check?

Not particularly, it's pretty straight-forward this one. However, there's still an issue with the modal header, but this is a more global error and should be fixed separately.

Why was this MR needed?

Two reasons:

1. The styling for this modal was broken after the bootstrap4 update.
2. A11y is improved by using the correct elements.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #47053 (closed)