Add a utility method to java.lang.Void for J2CL use.

Change-Id: I18b7e0d456fe80a9d7c0d118cd7bee40e7b13bb4

user/super/com/google/gwt/emul/java/lang/Void.java

diff --git a/user/super/com/google/gwt/emul/java/lang/Void.java b/user/super/com/google/gwt/emul/java/lang/Void.java
index 02222f6..014190f 100644
--- a/user/super/com/google/gwt/emul/java/lang/Void.java
+++ b/user/super/com/google/gwt/emul/java/lang/Void.java
@@ -28,4 +28,8 @@
   private Void() {
   }
 
+  // CHECKSTYLE_OFF: Utility Methods for unboxed Void.
+  protected static Void $create() {
+    throw new AssertionError();
+  }
 }