Crop handles "slip" out from under mouse cursor often

[tarngerine]

The hit area for detecting mousemove seems to be very sensitive (not to mention potential FPS drops), so the crop handles can easily become desynced from the mouse position

CleanShot.2022-08-24.at.16.48.19.mp4

I know this is a limitation of building in the browser, where mousemove events stop as soon as the mouse exits the hit area, but I wonder if

1. we can make the hit area the entire browser window — currently it stops at the bounds of the CropArea, which means when you start cropping from the edge you can often "lose grip" of the handles
2. Long term, change the implementation to be "absolute", storing the start mouse position on mousedown, and just checking the delta of the current mouse position compared to the starting position on mousemove. I've found this to feel better UX wise (and better for lower framerates) than accumulating the delta per event.