[Request] Shield Bonus as defence modifier

[NuptupTDOW]

If possible, could we get a modifier that can be added with effects that uses "shield" as it's value. Example system.defences.ac.shield so we can assign a shield bonus with effects on feats and features such as hafted defence that will properly not stack when not applicable?

If this already exists, could someone explain how to do it, because I am struggling.

[EndlesNights]

Thank the Fox!