this makes a keyboard widget update its keyInfoArray if its key has the `((descriptor))` format and one of the platform-specific configuration tiddlers with that descriptor-suffix changes
This is quite a big change: a new way to invoke action widgets.
The advantage is that it solves #2217 and #1564, a long running problem
that prevented us from adding action widgets to widgets that modify the
store.
This commit adds the new technique for the button and keyboard widgets,
but also extends the select widget to trigger action widgets for the
first time
Because of the refresh problems with the other widgets triggering action-widgets I am doing this one by itself. I hadn't included it before.
This shouldn't have any more problems than the button widget does, and any problems caused by it should be fixed by any fix we use for the button widget. See #1564 for more background
