test: update date-picker tests to not use async close helper

[web-padawan]

Description

UPD: actually there is a case with overlay blinking label click with the below changes, so I'll revert it for now.

The vaadin-overlay-close listener was added vaadin/vaadin-date-picker#498 - back then, date-picker has old clear button logic, which is no longer in use. As of today, the only case where that event actually contains sourceEvent is the "outside click" and the condition inside the listener appears to never be true.

Also, there is no need to wait for that event after changing close() method to set opened = false on the host (which is how other dropdown components work, e.g. vaadin-combo-box and vaadin-time-picker). In fact, unlike opening the overlay, closing is always synchronous so we can safely use datePicker.close() in tests.

Type of change

• Refactor

[web-padawan]

UPD: did some testing and with this change the date-picker blinks on label click, so the listener actually makes sense.
I will revert that part of the PR and add a test to ensure overlay is not closed. Other changes can be preserved though.

[sonarqubecloud]

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 SonarQube Cloud

[web-padawan]

Edited the PR to be only about test changes for now as the listener is actually useful.
I'll investigate if we can simplify handling label click taking the #7812 into account.

[vaadin-bot]

This ticket/PR has been released with Vaadin 24.6.0.beta3 and is also targeting the upcoming stable 24.6.0 version.