What problem does this address?

In #63896 we added a vertical displacement animation to zoom out mode, when dragging and dropping patterns between sections. In Safari these animations are a bit jerky and not as performant as other browsers.

@getdave summaried the issue as follows:

In relation to the jankyness of the separator animation in Safari. This is because the relatedTarget is not set when the dragleave event fires when leaving a block and entering the separator (caused by the animation).

The info on the draglave targets is as follows:

target - The EventTarget the pointing device exited from
relatedTarget - The EventTarget the pointing device entered to
As the relatedTarget is null we cannot detect that the drag has started over a separator (like we can in Chrome) an thus we cannot cancel the dragLeave handler on useBlockDropZone. This means that the hideInsertionPoint action is dispatched which causes the flicker.

The bug in Safari is - https://bugs.webkit.org/show_bug.cgi?id=66547

What is your proposed solution?

Unsure!