Add change vs input event description

The Synthetic Events docs for form events points to the Forms doc page as a reference for onChange, onInput, onInvalid, and onSubmit, but the Form page does not go into any detail about these events, and more importantly, how React's change and input events differ from the DOM events of the same name.

It appears a small note used to exist in the Form doc, but has been removed.

A short note about the change event exists in the DOM Elements doc. This was not an obvious place to look to for this information to me, and it does not address the input event. At the very least, this should probably be link to in the Synthetic Events doc, if no other changes are made.

I would like to see a more thorough description of the change and input events and when to use them in the Form doc.

Start with the Synthetic Events form-events section, the Forms documentation, and the DOM Elements onChange section linked in the issue. Compare their current coverage with the requested distinction between React's change and input events, and check the referenced pull request for prior wording. Done means the Forms documentation explains both events and when to use them, or clearly links to that explanation.