[Feature]: Snap arrow ends to grid
### What's the feature?

I probably have OCD (I don't know actually). I would like the start and end points of arrows to align to the grid when I draw them, not just when moving them!

### Where would you like this feature?

The tldraw.com website

### Contact Details

hey@nasso.dev

### Code of Conduct

- [X] I agree to follow this project's Code of Conduct