ComponentValidator ignores the set validator and creates a new one

Problem/Motivation

\Drupal\Core\Theme\Component\ComponentValidator has a method to setValidator
This allows contrib modules to change how the component validator behaves, including things like

• Add their own constraints (JSON Schema constraints, not Symfony validation constraints! So: \JsonSchema\Constraints\ConstraintInterface implementations, not \Symfony\Component\Validator\Constraint subclasses)
• Changing the constraint factory (again: JSON Schema constraints!)

These however are ignored by ::validateProps as it calls $validator = new Validator() instead of using the set validator

Steps to reproduce

Try to override the constraint factory by doing something like this:

$component_validator = new ComponentValidator();
    $component_validator->setValidator(new Validator((new Factory())->setConstraintClass('format', UrlHelperFormatConstraint::class)));

where UrlHelperFormatConstraint is a custom constraint.

Proposed resolution

Use the existing validator after resetting it

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet