Fix some issues with pulling system (#32145)

Fix some issues with pulling system (#32145)

Joints were created with pivots at object origin, causing unintuitive behaviour when an object was not centered on the origin. Now puts the pivots at the COM.
Joint limits were set based on fractions of the union of the AABB of objects, which did not make geometric sense. Now uses the pivot length with an additional [arbitrary] length.
Joints were created with a very low spring stiffness, which had a negligible effect most of the time but caused very unintuitive behaviour when the pulled object had a low mass (#28028) - disable the spring limit, and just use the hard min/max limits.

Co-authored-by: Eoin Mcloughlin <helloworld@eoinrul.es>