LibJS: Improve function hoisting across blocks

The parser now keeps track of a scope chain so that it can hoist
function declarations to the closest function scope.

Userland/Libraries/LibJS/AST.cpp

@@ -2377,4 +2377,9 @@ void ScopeNode::add_functions(NonnullRefPtrVector<FunctionDeclaration> functions
     m_functions.extend(move(functions));
 }
 
+void ScopeNode::add_hoisted_functions(NonnullRefPtrVector<FunctionDeclaration> hoisted_functions)
+{
+    m_hoisted_functions.extend(move(hoisted_functions));
+}
+
 }