[DOC] Add action docs to input and textarea helpers

I could not find any doc to explain how input helpers can send actions. I am not sure it has been forgotten or it was intentionally done.

I think, there are still some steps to be completed:

- [x] Add documentation to `TextSupport` properties of events (`focus-in`, `focus-out`...) like `action`.
- [x] Add missing tests of the different actionable events.


The docs are parsed completely unrelated to the actual JS, please do not actually define the property here (so it just ends up being the documentation block here).