Add whereSlug route validator

[xorock]

Currently, there are several methods in routing for input control (https://laravel.com/docs/10.x/routing#parameters-regular-expression-constraints - whereAlphaNumeric, whereNumber). A common practice is to use names in the URL, created with Str::slug e.g. /article/{slug}.
Perhaps a cool option would be to add a validator consistent with the one generated by Str::slug method?

[shaedrich]

I think, the problem is, that while Laravel has Str::slug() it doesn't implement sluggifying as a whole. In order to do that, Laravel would need an implementation like Spatie's laravel-sluggable