[11.x] Fluent numeric validation

[xoesae]

Description

This pull request introduces a new fluent numeric validation class, offering a more elegant and expressive way to define numeric validation rules.

Before this PR, numeric validation required string-based rules:

$rules = [
    'score' => 'numeric|integer|multiple_of:10|lte:some_field|max:100',
];

$validator = Validator::make($data, $rules);

if ($validator->fails()) {
    return $validator->errors();
}

To use the fluent numeric validation:

use Illuminate\Validation\Rule;

$rules = [
    'score' => [
        Rule::numeric()
            ->integer()
            ->multipleOf(10)
            ->lessThanOrEqual('some_field')
            ->max(100);
    ],
];

$validator = Validator::make($data, $rules);

if ($validator->fails()) {
    return $validator->errors();
}

[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!