[date-time-picker] Should not trigger validation when focus is moving inside the field

[vursen]

Description

date-time-picker triggers validation not only when focus moves away from the field but also when it is moving inside the field. As a result, if the field is required, it gets reported as invalid before the user has actually selected both date and time which is confusing from any perspective: UX, accessibility.

See the video for an illustration:

Screen.Recording.2022-09-02.at.14.24.51.mov

Expected outcome

I would expect the validation to be triggered only when focus moves out of the field.

Minimal reproducible example

<script type="module">
  import '@vaadin/date-time-picker';
</script>
<vaadin-date-time-picker
  label="Birth date and time"
  error-message="error-message"
  required
></vaadin-date-time-picker>

Steps to reproduce

1. Add the above snippet to an HTML page
2. Click on the date input.
3. Press Tab.

Environment

Vaadin version(s): 23.2, also affects older versions.
OS: Mac OS

Browsers

Issue is not browser related