Primitive node control widget visibility toggle

[0x473354]

Currently, primitive nodes always have control_after_generate or control_before_generate widget, and COMBO primitives also have a control_filter_list widget.

In my workflows I very rarely use anything other than fixed as I mostly use them for unifying widget values across multiple nodes. As such, these widgets can take up a significant amount of space, particularly when you have many primitive nodes or use primitives in group nodes. The existence of these widgets in group nodes when you don't want them is particularly aggravating as they can take up the majority of the area of the group node and cannot currently be hidden.

The most complete way to address this issue that I can think of would be to have a per-primitive-node option to toggle the aforementioned widgets that propagates through to group nodes. Other approaches would be to have another type of primitive node that does not have control widgets, or, to just address the group node issue, the ability to toggle the visibility of the control widgets in the group-node management window.