Add support for backdrop filter in QtQuick items

It would be nice to have support for backdrop filters in Qt, especially to implement effect like background blur or the acrylic effect from fluent design:

This effect is super common now. It's possible to be done in QtQuick 2.0 but this is technically complicated, and needs a lot of adaptation depending on the case to keep it performant.

Would be nice to have a way to do it easily in QtQuick so the Scene Graph optimize the effect.

The implementation is coming to web browser (on Firefox you need to enable a config), to have a preview of the css filter please see https://glassmorphism.com/