Enforce no-op on submit buttons with formmethod=dialog.

[geoffrey-eisenbarth]

Description

In Oct 2023, PR #1867 introduced a possible antipattern:

<dialog> 
  <form hx-post=/endpoint>
    <button formmethod=dialog>Submit and close</button>
  </form>
</dialog>

As a result of the above PR, current behavior is that clicking the button closes the dialog and submits the form (via hx-post). This is contrary to MDN docs on formmethod=dialog.

The author of that PR has since supported changing the behavior he introduced.

IMO people wishing to close a dialog and submit a form via HTMX at the same time should use e.g. hx-on:htmx:after-swap="event.target.closest('dialog').close().

There is a bit more conversation at PR #2753, which was my first attempt at this (PR was deleted because I couldn't git gud). Carson has approved this approach.

Corresponding issue: #1866

Testing

I have remove two tests and implemented one that I believe fits this situation, but I would appreciate it if someone could carefully review my test since I'm 100% on how the testing internals work.

Checklist

• I have read the contribution guidelines
• I have targeted this PR against the correct branch (master for website changes, dev for
  source changes)
• This is either a bugfix, a documentation update, or a new feature that has been explicitly
  approved via an issue
• I ran the test suite locally (npm run test) and verified that it succeeded