[TextArea] Implement the new validation behavior

[vursen]

An overview of the changes to be done

• Prevent the web component from setting itself to valid using ClientValidationUtil.
• Trigger constraint validation on client validated event
 (requires the HasClientValidation interface).
• Trigger binder validation on client validated event (requires the HasValidator interface).

See TextField for an example.

Constraints to be tested

• required
• minlength
• maxlength
• pattern

Additional context

All changes should be implemented behind the feature flag enforceFieldValidation on top of the existing implementation.

There are abstract classes AbstractValidationIT and AbstractValidationPage which are supposed to be extended when testing validation for a specific component.

Part of vaadin/platform#3066