[11.x] Fluent string validation

[mrvipchien]

This PR introduces a new fluent string validation, similar to the new fluent date (#53465) and numeric ([#54425]) validations.

Example Usage

use Illuminate\Validation\Rule;

public function rules()
{
    return [
        'foo' => [
            'required',
            Rule::string()->minLength(3)->maxLength(10)->alphaNumeric(),
        ],
        'bar' => Rule::string()->different('foo')->length(5)->uppercase(),
    ];
}

[shaedrich]

Should this really be part of the string validation and not of a separate URI validation rule like the email validation rule?

[shaedrich]

@mrvipchien @xoesae see #54519

[taylorotwell]

Thanks for your pull request to Laravel!

Unfortunately, I'm going to delay merging this code for now. To preserve our ability to adequately maintain the framework, we need to be very careful regarding the amount of code we include.

If applicable, please consider releasing your code as a package so that the community can still take advantage of your contributions!