…rst (nicwortel)

This PR was merged into the 6.1 branch.

Discussion
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[Routing] Document the Requirement constants in routing.rst

Fixes #16718

symfony/symfony#45528 by `@fancyweb` introduced the `Symfony\Component\Routing\Requirement\Requirement` enum in Symfony 6.1, as a solution for symfony/symfony#26524.

It was blogged about in https://symfony.com/blog/new-in-symfony-6-1-improved-routing-requirements-and-utf-8-parameters, but I couldn't find it anywhere in the Routing documentation.

This PR adds a small hint about the use of the `Requirement` enum for common route requirements:

![The Requirement enum contains a collection of commonly used regular-expression constants such as digits, dates and UUIDs which can be used as route parameter requirements.](https://user-images.githubusercontent.com/1055691/176497123-24b9bf6e-1b79-4385-baee-0eb132ae8944.png)

I'm open for suggestions to further improve this. I decided to use a small info block instead without code examples, because it doesn't seem to be a big feature and I'm not sure how well it is supported across all configuration formats. Let me know if you would like to see some code examples.

Commits
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571647d Document the Requirement constants in routing.rst