[dev nov 15] Start with code like this:

public class A {
    public static class B {}
}

Now in the Explorer, Cut B and Paste to the folder that A was in. B is
removed from A, and a new outer class B is made. Fine. Now Cut the new
B and Paste into the class A. It is pasted in. But now it looks like
this:

public class A {
    public class B {}
}

Since B was before the data transfer not a nonstatic inner class of A
(i.e. had no A.this reference), after the transfer it should be static
to keep its behavior as much the same as possible.