feat(developer): notify when .js is not included in the package when the keyboard supports touch/mobile

**Describe the bug**

This is a good to have, but probably not of high priority.

According to the issue [here](https://github.com/keymanapp/keyboards/issues/1916#issuecomment-1182456427), let's have Keyman Developer notify one that `.js` doesn't exist in the keyboard package while it supports mobile/touch devices.