Label scrubbing should use pointerLock and wrap around the screen

[maltenuhn]

Problem
Utopia input labels are scrubbable, but this scrubbing suffers from a number of issues:

• it is slow to update the inspector and canvas
• since the inspector is close to the edge of the screen, it sometimes means you run out of room (esp for large positive numbers like left)
• the mouse can trigger hover effects on the canvas or other inputs, which looks unprofessional

Solution

• Use the pointerLock API
• Draw a simulated mouse pointer
• wrap that pointer around the screen horizontally

Existing work

• for the performance, there's Canvas Performance: severe problems with dom-walker, MutationObserver and ResizeObserver #6067
• There's a draft PR: It barely scrubs #6195 with severe performance issues (and some notes / todos) - perhaps it just exacerbates existing performance problems?
• There's a working prototype implementation you can follow: https://github.com/maltenuhn/scrub-a-dub-dub/blob/master/src/DraggableRectangle.jsx