[PHP 8.2] Avoid Mbstring `HTML-ENTITIES` deprecation

[Ayesh]

In PHP 8.2, using the Base64, Uuencode, QPrint, and HTML Entity encodings are deprecated

There is one usage of the deprecated HTML-ENTITIES Mbstring encoder in \DiDom\Encoder::convertToHtmlEntities(), which relies on the buggy behavior of HTML-ENTITIES encoder, which does not encode characters that the htmlspecialchars function encodes.

This patch updates the direct HTML-ENTITIES encoding with three steps:

1. Encodes the string to UTF-8 from the given encoding $encoding
2. Encodes all HTML entities using htmlentities
3. Decodes special chars (<>'"&) using htmlspecialchars

Thank you.