Add a QString method to check for Emoji

emojis are very popular nowadays but Qt has almost no methods to work with them. Even so Qt had a lot of fixes to render emoji correctly.

So I propose to start with something simple. Like a check if a character sequence is an emoji.

Basically I want bool QString::isEmoji() const where it checks the accordance to https://unicode.org/Public/emoji/13.0/emoji-test.txt

This thing should also work with QStringRef.

Also it would be useful to have detection of emoji's group/subgroup/qualification. but it's rather something for other tasks. Just keep this in mind.