Fix Path2D editor not updating gizmos on selection in scene tree

[larspet]

Fixes #96392

You still need to release LMB before it updates, but the same goes for other editors, like the Polygon2D editor.

Is there even a reason for _handles and _edit to be called on mouse up after clicking a tree node, instead of on mouse down?
When selecting multiple nodes by holding CTRL, each additional node will be selected (and inspector updated etc.) on mouse down, but this is not the case for single selections.

Edit: Right, I just remembered that the delayed mouse up selection is needed for dragging nodes into the inspector.

[akien-mga]

Thanks!