Switch class loading logic in blackBoxWithJava tests

BoxWithJava tests now by default are loaded with the classloader which has
test's classpath in itself, as in the former ClassPathInTheSameClassLoaderTest

compiler/testData/codegen/boxWithJava/visibility/package/packageFun.java

@@ -0,0 +1,9 @@
+package protectedPack;
+
+import java.lang.String;
+
+public class packageFun {
+    String test() {
+        return "OK";
+    }
+}