fix: only fire opened change events on state change

[ugur-vaadin]

Description

As stated in a comment in the issue, a subdialog momentarily disconnects and reconnects when opened. This results in 2 extra opened-change events. The changes in those events are not actually reflected in the server-side opened state of the component. This PR prevents the event to be fired when there is no actual change in the state.

Fixes #5103

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.

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
2 Code Smells

No Coverage information
0.0% Duplication

[sissbruecker]

The root cause here is that the dialog WC toggles its opened state when it is disconnected / reconnected to the DOM as part of being moved to the parent dialog's overlay by the dialog renderer function. This is a result of the comment here: vaadin/web-components#3648 (comment), where we decided to avoid using a timeout to detect if the dialog stays disconnected.

In hindsight using a timeout might be better as we probably also want to avoid opened-changed events when just moving the dialog in the DOM. I've opened a PR (vaadin/web-components#5995) to fix the issue using a timeout, and will mark this as draft in the meantime. We can close this PR if we agree to use the timeout solution.

[sissbruecker]

Closing in favor of vaadin/web-components#5995