…nstraint class (loru88)This PR was submitted for the 3.4 branch but it was merged into the 2.7 branch instead (closes#24519).Discussion----------[Validator] [Twig] added magic method __isset()  to File Constraint class| Q             | A| ------------- | ---| Branch?       | 3.4 or master / 2.7, 2.8 or 3.3 <!-- see comment below -->| Bug fix?      | no| New feature?  | yes <!-- don't forget to update src/**/CHANGELOG.md files -->| BC breaks?    | no| Deprecations? | no <!-- don't forget to update UPGRADE-*.md files -->| Tests pass?   | yes| Fixed tickets |#24512  <!-- #-prefixed issue number(s), if any -->| License       | MIT| Doc PR        | symfony/symfony-docs#... <!--highly recommended for new features-->In my project I get assert constraints from one of my entity and I use this value in my front end via Twig.I faced a problem with the property $maxSize of the File Constraint.As this property is protected I cannot access it via Twig because the magic method __isset is missing, as I read in twig documentation.<!--- Bug fixes must be submitted against the lowest branch where they apply  (lowest branches are regularly merged to upper ones so they get the fixes too).- Features and deprecations must be submitted against the 3.4,  legacy code removals go to the master branch.- Please fill in this template according to the PR you're about to submit.- Replace this comment by a description of what your PR is solving.-->Commits-------9efb765 [Validator] added magic method __isset()  to File Constraint class