[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:

- [ ] Add documentation to `TextSupport` properties of events (`focus-in`, `focus-out`...) like `action`.
- [ ] Add missing tests of the different actionable events.