[Feature Request] Allow material swapping on Arcs

[UrkiMimi]

I thought of this when I created the request for math operations on arcs, but since that dream is (mostly) dead. I thought this would be a better compromise.

This will allow you to change the material of an arc on a given track to whatever you want. This includes texture replacements, vertex shaders, etc. The JSON syntax I'm thinking of should be similar to AssignObjectPrefab, but instead, you're using material.

{
  "b": 70.0,
  "t": "AssignArcMaterial",
  "d": {
    "track": ["arcGlitch", "fade"],
    "material": "assets/path/to/cool/vertex/shader/material.mat"
  }
}

this is totally not massive cope with the custom line renderer that arcs use

[Swifter1243]

+1 on this! though it makes infinitely more sense to use the existing AssignObjectPrefab event.