add a normalize() method for unicode normalization forms

[Wes0617]

stuff already exists in the class Normalizer but would be handy to have it in this class as well. could look like JS's normalize() https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/normalize

echo u($str)->normalize(UString::NFKC)->subString(0, 4);

[hikari-no-yume]

Easy access to normalisation is quite essential. A lot of people neglect it. So, I support this in some form.