feature(symfony): Add CSS Color Schema Restriction for Property Validation

[SebLevDev]

Description

This PR introduces the PropertySchemaCssColorRestriction class, which generates a regular expression (pattern) for validating CSS color values in API Platform property schemas, based on the Symfony CssColor constraint.

Technical Details

Supports multiple CSS color formats (hex, rgb, rgba, hsl, hsla, named colors, etc.).
Dynamically builds a single regex pattern combining all allowed formats, suitable for OpenAPI/JSON Schema documentation.

Example

With a given resource Theme

#[ApiResource]
class Theme
{
    private ?int $id = null;

    #[Assert\NotNull]
    #[Assert\CssColor(
        formats: Assert\CssColor::HEX_LONG,
    )]
    public ?string $backgroundColor = null;
}

The impact in the OpenApi Schema provide

{
  "Theme": {
    "type": "object",
    "properties": {
      "id": {
        "type": "integer",
        "readOnly": true
      },
      "backgroundColor": {
        "type": "string",
        "pattern": "^#(?:[0-9a-f]{6})$",
      }
    },
    "required": ["backgroundColor"]
  }
}

[soyuka]

looks nice, could you maybe explain how this is used? (or open a doc PR)

It'd be nice to add some tests (can also be functional testing)

[SebLevDev]

I've updated the PR description to include an example of how to use the constraint in an entity.
I've also added a unit test to cover the PropertySchemaCssColorRestriction logic.
Let me know if anything else is needed!

[soyuka]

awesome thanks!