[php-src] PR #25288: Fix GH-25284: quoted_printable_encode splits UTF-8 characters

Pull Request: https://github.com/php/php-src/pull/25288 Author: lazerg The soft line break check treated UTF-8 continuation bytes (0x80 to 0xBF) like 2-byte lead bytes, so each one reserved room for another =XX that never comes. When the last byte of a character landed exactly at the line limit, it got pushed to the next line and the character was split. The lead byte already reserves room for the whole sequence, so continuation bytes now only break when they don't fit themselves, same as single bytes. quoted_printable_encode_002.phpt had the split characters in its expected output, so I updated it. Fixes #25284