mb_strwidth behavior changed

Due to this commit, the documentation for mb_strwidth should be changed: https://github.com/php/php-src/commit/d8c785b894e1a4ed9793d71cad02330cb0034faa?

This function now returns the proper width of a multibyte string starting with php 8.1.  For example:

For php <= 8.0:

echo mb_strwidth('🏆');

returns: 1


For php >= 8.1:

echo mb_strwidth('🏆');

returns: 2