feat: draft freehand highlighter

[DerpDays]

This is will add a freehand highlighter as the default (with shift to align it), and then have a selection highlight (like there currently is) accessible by pressing ctrl whilst on the highlighter, since this was suggested at some point (though since currently the highlighter tool is the selection it might make more sense to make the freehand one accessible through ctrl instead), currently this is just draft and needs quite a bit of cleanup.