QML JS Multiline Strings

Hi,

it would be nice to have "multiline strings" in js files.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals

I hope its ok to open a seperate ticket for it, because this is mentioned in a bigger feature request https://bugreports.qt.io/browse/QTBUG-47735 and part of it seems already done https://codereview.qt-project.org/#/c/215213/