Description:
------------
mb_check_encoding() takes either string or array as first parameter. It seems that with added support for arrays we might have lost the ability to provide objects with __toString() methods as input. I would expect that when object of a class having __toString() method is provided as input for mb_check_encoding() then the result of __toString() will be used. Instead we currently get the following warning: Warning: mb_check_encoding(): Input is something other than scalar or array in /sandbox/mb-check-encoding-invalid-input.php on line 11

Possible related commit: https://github.com/php/php-src/commit/b651b967383082de0f9c15ad6fcb36dda4082b0d
Possible related part of code: https://github.com/php/php-src/blob/5d6e923d46a89fe9cd8fb6c3a6da675aa67197b4/ext/mbstring/mbstring.c#L4823-L4844

P.S. Also take note that documentation at https://www.php.net/manual/en/function.mb-check-encoding.php does not mention array as being supported first argument type.

Test script:
---------------
<?php

class Foo
{
    public function __toString()
    {
        return 'string_representation';
    }
}

mb_check_encoding(new Foo, 'UTF-8');

Expected result:
----------------
Script runs in both PHP 7.1.32 and PHP 7.3.9 without warnings. When we remove __toString() method then we get warnings in both PHP versions.

Actual result:
--------------
Script runs without warnings in PHP 7.1.32 but gives (unexpected) warning "Input is something other than scalar or array" in PHP 7.3.9. When we remove __toString() method then PHP 7.1.32 gives warning "mb_check_encoding() expects parameter 1 to be string, object given" and PHP 7.3.9 gives warning "Input is something other than scalar or array"