[9.x] Add RequiredIfAccepted validation rule

[pascalbaljet]

This PR adds a required_if_accepted rule. The field under validation must be present and not empty if the anotherfield field is accepted ("yes", "on", 1, or true).

Validator::make([
    'is_company'   => '1',
    'company_name' => 'Apple',
], [
    'is_company'   => 'required|boolean',
    'company_name' => 'required_if_accepted:is_company',
]);

[pascalbaljet]

The PHP 8.0 test fails because of an unrelated Redis error, but I can't restart the job :)

[garygreen]

Couldn't you just do:

required_if:is_company,on

This PR adds a bool-like checker which I'm not personally a fan of, as it causes issues with having to handle "on" "yes" which is quirky. Often better to just use very explicit defines values - I prefer 0 1 for true/false on/off as it's easier to handle.

[pascalbaljet]

This PR adds a bool-like checker which I'm not personally a fan of, as it causes issues with having to handle "on" "yes" which is quirky. Often better to just use very explicit defines values - I prefer 0 1 for true/false on/off as it's easier to handle.

You could argue the same for the accepted rule. This new rule combines the accepted and required rules. It's just a little shortcut.

[garygreen]

You could argue the same for the accepted rule. This new rule combines the accepted and required rules. It's just a little shortcut.

I'm not a fan of the accepted style rules either - what does it mean to be "accepted"? "true" "false" "approved" "accepted" ? This PR reminds me of #43955 - these general validation rules have a great degree of feature creep over time and can become a source of weird bugs. Honestly, it's better to just define explicitly what values you expect.