Add additional protected visibility prototype test

See https://github.com/php/php-src/pull/3993 for context.

Zend/tests/grandparent_prototype.phpt

@@ -0,0 +1,26 @@
+--TEST--
+Protected visibility test case with a grandparent prototype
+--FILE--
+<?php
+
+class A {
+    protected function test() {}
+}
+class B extends A {
+    public function test2($x) {
+        $x->test(); // Uncaught Error: Call to protected method D::test() from context 'B'
+    }
+}
+class C extends A {
+    protected function test() {}
+}
+class D extends C {
+    protected function test() {
+        echo "Hello World!\n";
+    }
+}
+(new B)->test2(new D);
+
+?>
+--EXPECT--
+Hello World!