Have file.modpath() run the OCI url when called from OCI

[obeleh]

I was discussing file.modpath() with @zong-zhe here

I was wondering what it would return as I was trying to rely on it's behavior in a module: example

On one hand I want the behavior of a module not to change when I release it to an OCI registry. On the other hand, I don't want it to "lie" either. So I think the modpath for oci://something.com/a should be "oci://something.com/a"

Things that I think would complicate it:

• If one was trying to find out the "parent directory". I think it should return "oci://something.com" but getting the parent directory of "oci://something.com" would be equivalent to getting the parent directory of /

[Peefy]

cc @zong-zhe @He1pa