Establish the RoadIntersection class

[TheDuckCow]

Stepping stone to create the intersection support. This will have to cover:

• Allowing roadpoint children
• Having options to generate/refresh roadpoint children, so we can generate reference geometry in the scene without there being a road network
• This also means performing cleanup or propagating regeneration if needed from a RoadNetwork parent, should one exist.
• Create a simple, efficient visualizer which draws dotted lines from each RoadPoint to the RoadIntersection it connects to. This way it's easy to see what you've already hooked up.
  • This visualizer should ideally not use immediate geometry (which is slow), and would only show when in the prefab scene itself (not once in a scene with a RoadNetwork).
• The intended use is to have this node be the root node of a scene, but should also work if added as a hierarchy in a larger scene as well. Children RoadPoint should know to not propagate past the boundaries appropriately.

Out of scope for this task:

• Actual procedural intersections - will be created as follow up tasks. See https://github.com/TheDuckCow/godot-road-generator/issues/121

[TheDuckCow]

Interesting UX idea on intersections, not sure it's really relevant since we'll inherently have a primary container for the intersection itself anyways. Could be interesting to see more about this game (Tropico) and how it handles UX especially since it's for mobile.

[TheDuckCow]

Here's another video (this time, an Unreal tool) showing intersections as just chunks you can place into the world. With its drag and drop nature, it seems like this one is actually quite nice to work with since it seems to not require/enforce very specific hierarchy structure (though the tools to actually form the connections aren't that great, all being done from side panels + picker tools back and forth).