LibJS: Make the AST reference-counted

This allows function objects to outlive the original parsed program
without their ScopeNode disappearing.

Libraries/LibJS/Runtime/ScriptFunction.cpp

@@ -24,6 +24,7 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <LibJS/AST.h>
 #include <LibJS/Interpreter.h>
 #include <LibJS/Runtime/ScriptFunction.h>
 #include <LibJS/Runtime/Value.h>

Libraries/LibJS/Runtime/ScriptFunction.h

@@ -44,7 +44,7 @@ private:
     virtual bool is_script_function() const final { return true; }
     virtual const char* class_name() const override { return "ScriptFunction"; }
 
-    const ScopeNode& m_body;
+    NonnullRefPtr<ScopeNode> m_body;
     const Vector<String> m_parameters;
 };