[Platform] Backed Enums Support for Tool Arguments and Structured Output

[chr-hertel]

Json Schema supports defining enums on properties, which is even supported with our #[With] attribute to be configured explicitly. But it would also be great to support this without attribute, when a Backed Enum is used as type:

enum Mode: string
{
    case AND = 'and';
    case OR = 'or';
}

class MySearchTool
{
    public function __invoke(array $searchTerms, Mode $mode): array
    {
        // ...
    }
}