move: convert nested classes to the top level files even for multiple classes selected

EA-81558 - assert: PsiJavaDirectoryImpl.checkAdd

java/java-tests/testData/refactoring/moveClassAndFile/nestedClassesInFile/after/t/MyClass.java

@@ -0,0 +1,5 @@
+package t;
+class MyClass {
+  public static class F1 {}
+  public static class F2 {}
+}