[firefox] Fix the pointer getting stuck down when you press the control key (#1390)

This PR fixes a bug in firefox where the pointer can get stuck down
while pressing the control key.

It achieves this by taking a previous fix (specifically for
`useShapeEvents`), and it applies the fix at a deeper level (within
`app.dispatch`).

## Before
![2023-05-16 at 15 33 02 - Crimson
Coyote](https://github.com/tldraw/tldraw/assets/15892272/7d4b5bb1-a2e5-400c-9935-fddcc9645e52)

## After
![2023-05-16 at 15 34 03 - Purple
Panda](https://github.com/tldraw/tldraw/assets/15892272/34a598b2-bf6d-4847-8ce9-a3d52c418174)

### Change Type

- [x] `patch` — Bug Fix

### Test Plan

1. Use firefox.
2. On the canvas... pointer down (to start a selection box).
3. Control key down.
4. Pointer up.
5. Make sure that that the selection box is gone.

^ Repeat the above for:
Pointer down on a shape.
Pointer down on a handle.

### Release Notes

- [Firefox] Fixed a bug where the pointer could get stuck down when the
control key is held down.

packages/editor/src/lib/hooks/useCanvasEvents.ts

@@ -43,7 +43,7 @@ export function useCanvasEvents() {
 
 			function onPointerUp(e: React.PointerEvent) {
 				if ((e as any).isKilled) return
-				if (e.button !== 0 && e.button !== 1 && e.button !== 5) return
+				if (e.button !== 0 && e.button !== 1 && e.button !== 2 && e.button !== 5) return
 				lastX = e.clientX
 				lastY = e.clientY