[terrible] Firefox: Allow scrolling on keyboard shortcuts dialog (#2974)

This PR lets firefox users scroll the keyboard shortcuts dialog
**horizontally**.
This isn't a real solution, just a plea for help for any ideas on how to
fix this in a better way.

Firefox users haven't been able to scroll the keyboard shortcuts dialog
for a long time.
The problem is that firefox handles overflowing column content
differently to other browsers. Most browsers overflow *downwards*, but
firefox overflows *sideways*, and there's no CSS property to control
that behaviour.
 
### Change Type

- [x] `patch` — Bug fix
- [ ] `minor` — New feature
- [ ] `major` — Breaking change
- [ ] `dependencies` — Changes to package dependencies[^1]
- [ ] `documentation` — Changes to the documentation only[^2]
- [ ] `tests` — Changes to any test code only[^2]
- [ ] `internal` — Any other changes that don't affect the published
package[^2]
- [ ] I don't know

[^1]: publishes a `patch` release, for devDependencies use `internal`
[^2]: will not publish a new version

### Test Plan

1. Open the keyboard shortcuts dialog on firefox.
2. Try to scroll the dialog to see overflowing content. More visible on
smaller screens.

- [ ] Unit Tests
- [ ] End to end tests

### Release Notes

- Add a brief release note for your PR here.

Co-authored-by: Steve Ruiz <steveruizok@gmail.com>

packages/tldraw/src/lib/ui.css

@@ -1492,6 +1492,9 @@
 	column-gap: var(--space-9);
 	pointer-events: all;
 	touch-action: auto;
+
+	/* Terrible fix to allow firefox users to scroll the dialog */
+	overflow-x: auto;
 }
 
 .tlui-shortcuts-dialog__body__tablet {