Crash in AbstractAtmComboVisitor: AnnotatedTypeMirrors aren't structurally equal.

[cushon]

I think this is the last distinct failure I'm seeing in my testing at head, with #4866 and #4875 patched in.

abstract class L<T> {
  protected L(A<T> c) {}
}

class A<T> {
  static class B<T> {
    public B() {}

    A<T> build() {
      throw new AssertionError();
    }
  }
}

class T {
  private final class I extends L<Object> {
    private I() {
      super(new A.B<>().build());
    }
  }
}

error: AnnotatedTypeMirrors aren't structurally equal.
    type1 = AnnotatedTypeVariable( T extends Object )
    type2 = AnnotatedDeclaredType( Object )
    visitHistory = org.checkerframework.framework.type.StructuralEqualityVisitHistory@181098bf
  ; The Checker Framework crashed.  Please report the crash.
  Compilation unit: T.java
  Last visited tree at line 18 column 7:
        super(new A.B<>().build());
  Exception: java.lang.Throwable; java.lang.Throwable
        at org.checkerframework.javacutil.BugInCF.<init>(BugInCF.java:22)
        at org.checkerframework.framework.type.visitor.AbstractAtmComboVisitor.defaultAction(AbstractAtmComboVisitor.java:52)
        at org.checkerframework.framework.type.StructuralEqualityComparer.defaultAction(StructuralEqualityComparer.java:56)
        at org.checkerframework.framework.type.StructuralEqualityComparer.defaultAction(StructuralEqualityComparer.java:29)
        at org.checkerframework.framework.type.visitor.AbstractAtmComboVisitor.visitTypevar_Declared(AbstractAtmComboVisitor.java:543)
        at org.checkerframework.framework.util.AtmCombo.accept(AtmCombo.java:587)
        at org.checkerframework.framework.type.StructuralEqualityComparer.areEqual(StructuralEqualityComparer.java:93)
        at org.checkerframework.framework.type.StructuralEqualityComparer.areEqualInHierarchy(StructuralEqualityComparer.java:105)
        at org.checkerframework.framework.type.DefaultTypeHierarchy.areEqualInHierarchy(DefaultTypeHierarchy.java:236)
        at org.checkerframework.framework.type.DefaultTypeHierarchy.isContainedBy(DefaultTypeHierarchy.java:311)
        at org.checkerframework.framework.type.DefaultTypeHierarchy.isContainedMany(DefaultTypeHierarchy.java:537)
        at org.checkerframework.framework.type.DefaultTypeHierarchy.visitTypeArgs(DefaultTypeHierarchy.java:507)