docs(ngSubmit): ngSubmit also works with the `data-action`/`x-action` attributes

The documentation states only the "action" attribute triggers this, which is incorrect. When using
the attribute "data-action" (as for AJAX control, attempting to bypass the "action" attribute but
still make it obvious what its for), Angular thinks this is also classified as "action" and
continues with the page submission.

Closes #6196