Fix PHP 8.2 utf8_encode() Deprecated issue on HandlerFor403AccessDenied class

Problem/Motivation

This was addressed in PHP 8.2 to fix the utf8_encode() compatibility issue (3380518), but it may have inadvertently removed the support base path commit.

Proposed resolution

Follow the recommendation of official php documentation and replace the use of utf8_encode() with the mb_convert_encoding() function.