Polyfill utf8_encode use for php8.2+ compatibility

[elhardoum]

Describe the bug

With php8.2 released a couple weeks ago, and since this library supports "php": ">=5.6.0", I think it's time to add a polyfill for the deprecated function utf8_encode:

stripe-php/lib/Util/Util.php

Line 88 in f672444

return \utf8_encode($value);

Symfony has a nice polyfill library that can be used: https://github.com/symfony/polyfill/blob/-/src/Php72/Php72.php#L24

To Reproduce

1. Use php8.2
2. Run the unit tests, or simply call \Stripe\Util\Util::utf8('test')

Expected behavior

It should throw a deprecation notice error

Code snippets

No response

OS

macOS

PHP version

PHP 8.2

Library version

latest

API version

latest

Additional context

No response

[anniel-stripe]

Thanks for flagging!

I've opened a PR to address this by following the steps in https://php.watch/versions/8.2/utf8_encode-utf8_decode-deprecated#utf8_encode-any-mbstring , since I believe we actually want to convert any string to UTF-8 encoding, not just those encoded in ISO-8859-1.

Edit: Looks like the encoding detection is imperfect, so switched to https://php.watch/versions/8.2/utf8_encode-utf8_decode-deprecated#utf8_encode-iso8859-mbstring instead.