[Validator] Added date support to comparison constraints and Range

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #7766, #9164, #9390, #8300
| License       | MIT
| Doc PR        | TODO

This commit adds frequently requested functionality to compare dates. Since the `DateTime` constructor is very flexible, you can do many fancy things now such as:

```php
/**
 * Only accept requests that start in at least an hour.
 * @GreaterThanOrEqual("+1 hours")
 */
private $requestedSurgeryDate;
```