Linked Group Inputs

It would be very useful to have linked inputs, for inputs that are dependent on one another. This would allow for node setups that use systems of equations, and can be customized using any of those equations variables.

A common example is in image editors when you can toggle aspect ratio locking, so that editing one pixel dimension edits the other proportionally.

Similarly, there could be a button on linked inputs that lets you toggle whether an input is allowed to be changed by its links.

This can reuse several ui elements from gizmos, including double links and the icon location on group inputs that indicates a value is controlled by a gizmo (probably with a different icon though).