fromCodePoint function
Convert a Unicode code point to a string.
Equivalent to JavaScript's String.fromCodePoint().
Implementation
String fromCodePoint(int code) {
if (code <= 0xFFFF) return String.fromCharCode(code);
code -= 0x10000;
return String.fromCharCodes([
(code >> 10) + 0xD800,
(code & 0x3FF) + 0xDC00,
]);
}