Apply margin to camera and shape in SpringArm3D

[Chronos-W]

Fixes !76220

Currently, margin is only being used when neither a Camera3D is the SpringArm3D's child node nor when a shape has been set, which doesn't seem to align with the described behavior in the docs https://docs.godotengine.org/en/stable/classes/class_springarm3d.html#class-springarm3d-property-margin.

After this change, in addition to the scenario it currently works for, the margin value will also apply when the child node of the SpringArm3D is a Camera3D node, and it will apply when there's a shape set for SpringArm3D.

And for those who were wondering, SpringArm3D already has an if condition for handling a child node with Camera3D, so I'm just adding this application of margin there as well.

springarmmarginfix.zip

• Three SpringArm3D nodes: one with Camera3D as child node, one that uses SpringArm3D's shape, and one that does neither of the previous two so it uses a raycast. Margin should apply to all three.