LibJS: Implement ClassExpression::generate_bytecode()

...and use that in ClassDeclaration::generate_bytecode().

Userland/Libraries/LibJS/AST.h

@@ -1373,6 +1373,7 @@ public:
 
     virtual Completion execute(Interpreter&, GlobalObject&) const override;
     virtual void dump(int indent) const override;
+    virtual Bytecode::CodeGenerationErrorOr<void> generate_bytecode(Bytecode::Generator&) const override;
 
     bool has_name() const { return !m_name.is_empty(); }
 

Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp

@@ -1337,10 +1337,17 @@ Bytecode::CodeGenerationErrorOr<void> SwitchStatement::generate_bytecode(Bytecod
     return {};
 }
 
-void ClassDeclaration::generate_bytecode(Bytecode::Generator& generator) const
+Bytecode::CodeGenerationErrorOr<void> ClassDeclaration::generate_bytecode(Bytecode::Generator& generator) const
 {
-    generator.emit<Bytecode::Op::NewClass>(m_class_expression);
-    generator.emit<Bytecode::Op::SetVariable>(generator.intern_identifier(m_class_expression.ptr()->name()));
+    TRY(m_class_expression->generate_bytecode(generator));
+    generator.emit<Bytecode::Op::SetVariable>(generator.intern_identifier(m_class_expression.ptr()->name()), Bytecode::Op::SetVariable::InitializationMode::Initialize);
+    return {};
+}
+
+Bytecode::CodeGenerationErrorOr<void> ClassExpression::generate_bytecode(Bytecode::Generator& generator) const
+{
+    generator.emit<Bytecode::Op::NewClass>(*this);
+    return {};
 }
 
 Bytecode::CodeGenerationErrorOr<void> ThisExpression::generate_bytecode(Bytecode::Generator& generator) const