feat(web): implement method stubs in `KMXKeyboard` 🎼

`KMXKeyboard` has several methods that are only stubs at the moment. [isChiral](https://github.com/keymanapp/keyman/blob/df0cd0c3f95cb4898e44538ec3a93a718bf3d882/web/src/engine/src/keyboard/keyboards/kmxKeyboard.ts#L87)