bug(web): Control-by-Control Example not working properly

The [Control-by-Control Example](https://help.keyman.com/developer/engine/web/18.0/guide/examples/__control-by-control.html) shows several problems in the Subject field which doesn't work as announced on the label:

1. Keyboard does show on desktop browsers. It's expected to be "off".
2. Keyboard in Subject field defaults to Devanagari keyboard. Expected is to have the system keyboard activated. Note that there is no "English" keyboard anymore as in previous versions.
3. Occasional mismatch in Message body field between the displayed OSK (Lao) and the keyboard shown as active in the dropdown:

The [last properly working version](https://help.keyman.com/developer/engine/web/12.0/guide/examples/control-by-control) was with Keyman 12.