ext-mbstring should be required

[alecpl]

Here's why:

1. Masterminds\HTML5\Parser\CharacterReference::lookupDecimal() uses mb_decode_numericentity() unconditionally.
2. Looking at Masterminds\HTML5\Parser\UTF8Utils::convertToUTF8() either iconv or mbstring must be available (if the input encoding is not 'auto').

This would allow to:

1. Get rid of iconv() use. In my experience mbstring is really a better solution.
2. Remove use of utf8_decode() which is not really valid and not needed when mbstring is available.
3. Get rid of the fallback code.

[alecpl]

Actually utf8_decode() is deprecated in PHP 8.2, and will be removed later. So, this is more like a bug now.

[goetas]

sorry for the late reply. makes sense what you are suggesting. would be happy to see a PR