Add support for `event.code`

While it may prove impossible to smooth over all OS / keyboard layout differences in `event.key`, providing access to mapping hotkeys to an [`event.code`](https://developer.mozilla.org/en-US/docs/Web/API/UI_Events/Keyboard_event_code_values) may help in some situations (for example WASD navigation)

[VS Code allows this via wrapping the code in `[]`](https://code.visualstudio.com/docs/getstarted/keybindings#_keyboard-layoutindependent-bindings): for example `[KeyA]` would match on `event.code === "KeyA"`.

This allows for some flexibility to map shortcuts to physical locations on the keyboard (eg WASD navigation etc.)

未指定文件或测试。首先定位现有的 event.key 快捷键匹配路径，并检查方括号中的绑定如何表示 [KeyA] 这类 event.code 值。完成的标准是：物理按键绑定能够用于 WASD 导航等示例，同时不会破坏现有快捷键。

由索引模型根据 Issue 内容生成。