feat: date time picker validation improvements

[ugur-vaadin]

Description

This PR implements DateTimePicker validation improvements for the Flow counterpart. The changes include:

• Use the new unparsable-change event from the web component
• Replace the validated event
• Prevent multiple validations during a single round-trip
• Improve validation consistency similar to the web component
• Postpone validation during navigation between DP and TP unless we are certain the value will be invalid (unless it is invalid or out of the range set using mix/max)
• Introduce a dedicated error message for incomplete values
• Handle the input element value changes caused by programmatically setting values

Based on the prototype.

Depends on vaadin/web-components#8986.

Part of #6697

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

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
4.0% Duplication on New Code

See analysis details on SonarQube Cloud

[vursen]

Could you please explain why this additional event is necessary? What scenario is it intended to cover?

[vursen]

This approach might not be correct since isInvalid() will still report true on the server side until the next round-trip occurs. I explored this a bit on my own and may have found a solution that avoids a round-trip: cbd6285. Please let me know if you see any issues with it.