Allow creating a VisualShader node group from a selection

[Geometror]

This is a follow-up to #99404, adding one important UX improvement that speeds up node group creation significantly.
As always, this was a bit more sophisticated than anticipated.

Detailed changes:

• Adds a context menu option ("Make Group") for creating a group based on the current selection in the VisualShader editor
  • Replaces the selection after validating (to prevent cycles or forbidden nodes moving in) with a node group instance (everything stays connected, so the operation is seamless); undo/redo works of course
  • Multiple connections from the same output port share one group port; group ports are sorted based on the position of the source nodes to minimize "entanglement"; group port names are based on the inner port they are connected to (with a fallback to that node's caption).
• Refactoring along the way:
  • Made NodeMenuOptions and ConnectionMenuOptions enum class to avoid the MAKE_GROUP name clash (+ we want to move to enum class in general)
  • Refactor node deletion a bit (use LocalVector instead of List)

Notes:

• A remaining TODO is to add a shortcut (Ctrl + G) for this, but that might conflict with grouping in the 2D/3D editor (need to investigate)
• I'd really like to deprecate VisualShaderNodeGroupBase since it's a relic from the past. Ideally the Expression node should be overhauled to use the same mechanisms for port management as node groups.
• I have a refactor/cleanup PR for the port expansion code in the works which should get rid of ~300 LOC.

AI Disclosure: AI was used as part of a review pass at the end; resulting changes were done manually or in the form of surgical instructions.

[LiveTrower]

I was just about to make a proposal about this.

[AThousandShips]

Can this use iterate_children?