fix: prevent setting both login listeners and form action

[mcollovati]

Description

Setting both login listeners and form action can cause unexpected behaviors because of concurrent processing of form submission processing and login event.
For example, if form submission ends in a session ID change and a redirect to a different page, the UIDL request may fail with a session expiration response, causing the Flow client to reload the page and potentially cancel the ongoing redirection.
In addition, after from submission, the login event would be sent to a dismissed UI.
This change prevents setting both action and login listeners throwing an exception.

References vaadin/flow#12640

Type of change

• Bugfix
• Feature

Checklist

• I have read the contribution guide: https://vaadin.com/docs/latest/contributing/overview
• I have added a description following the guideline.
• The issue is created in the corresponding repository and I have referenced it.
• I have added tests to ensure my change is effective and works as intended.
• New and existing tests are passing locally with my change.
• I have performed self-review and corrected misspellings.
• I have not completed some of the steps above and my pull request can be closed immediately.

Additional for Feature type of change

• Enhancement / new feature was discussed in a corresponding GitHub issue and Acceptance Criteria were created.

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud