[Validator] Pass context to expressions used in When constraints

[fabpot]

Q	A
Feature PR	symfony/symfony#58512
PR author(s)	@KoNekoD
Merged in	7.2

We created this issue to not forget to document this new feature. We would really appreciate if you can help us with this task. If you are not sure how to do it, please ask us and we will help you.

To fix this issue, please create a PR against the 7.2 branch in the symfony-docs repository.

Thank you! 😃

[KoNekoD]

Created Pull Request

#20314

Please advise where is the best place to add documentation on how to use context? I think we should create a separate paragraph with declaration of 2 classes, where the child class through context.root checks the parent's property to activate its validation