Remove codegen tests with Java, move testData to boxWithJava/

There'll be a single generated test class like
BlackBoxCodegenTestGenerated

compiler/testData/codegen/boxWithJava/staticFun/classWithNestedEnum.java

@@ -0,0 +1,7 @@
+package test;
+
+public class classWithNestedEnum {
+    public enum E { ENTRY }
+    
+    public static String foo() { return "OK"; }
+}