Fix PHP 8.2 deprecations

[seanBlommaert]

Because of the misleading function names, lack of error messages and warnings, and the lack of support for character encodings other than ISO-8859-1, utf8_encode and utf8_decode functions are deprecated in PHP 8.2.

This is being used in \DaveChild\TextStatistics\Text::cleanText()

We can replace it with the code below, or maybe see if we can remove it?
$strText = mb_convert_encoding($strText, 'ISO-8859-1', mb_detect_encoding($strText));

[seanBlommaert]

I see there already is a PR for this: #56 (and more 8.2 deprecations).