[ic-side-navigation] escape doesn't close the menu on mobile top bar

## Summary of the bug
When you view side nav on a small device and open up the menu, pressing escape doesn't close the menu.

You can currently close the menu by hitting enter/space or clicking close, but I feel this should also be added in as another method of closing the menu.

## 🪜 How to reproduce
Tell us the steps to reproduce the problem:
1. Go to any side nav example
2. Reduce screen size so that the top bar behaviour shows
3. Open up the menu
4. Try to escape and see the error

## 🧐 Expected behaviour
Pressing escape should close the menu.

Start with any side nav example, reduce the screen size until the mobile top bar appears, open the menu, and reproduce the Escape-key failure. Inspect the mobile menu handling for ic-side-navigation; done means pressing Escape closes the open menu, matching the existing Enter, Space, and close-button behavior.

Written by the indexing model from the issue text.