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

[GCHQ-Developer-530]

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.

[MI6-255]

Good practice, not a violation

[MI6-255]

Is there a complication if you press escape when focused on another element e.g. a form, we wouldn't want it to close the side navigation?