Feature request: String.prototype.codePointAt() / String.fromCodePoint() [ECMAScript2015]

Those are part of ECMAScript 2015 spec (aka ES6), so this is a tiny portion of QTBUG-47735.

The difference from already implemented String.prototype.charCodeAt() / String.fromCharCode() is UTF-16 surrogate pair support, mapping those to and from a single code point integer value.

MDN:

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/codePointAt
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/fromCodePoint

Spec:

• http://www.ecma-international.org/ecma-262/6.0/#sec-string.prototype.codepointat
• http://www.ecma-international.org/ecma-262/6.0/#sec-string.fromcodepoint

Polyfill:

• https://github.com/mathiasbynens/String.prototype.codePointAt
• https://github.com/mathiasbynens/String.fromCodePoint