[java-completion] IDEA-335904 Completion in enhanced switch for enum

- offer classes and interfaces
- offer `default` after `case null,`

GitOrigin-RevId: f1d0567efeafcd5320db88089bab7eb1dbe17b9f

java/java-tests/testData/codeInsight/completion/normal/DefaultAfterNullInJava20_after.java

@@ -0,0 +1,11 @@
+class Main {
+  enum Numbers{ONE, TWO}
+
+  private static void testEnum2(Object r2) {
+    switch (r2) {
+      case Numbers.ONE:
+        break;
+      case null, <caret>
+    }
+  }
+}