Wrong type of font.weight property in Qt Quick

The font.weight property in Qt Quick was set to be an enumeration, so it can only represent the font weight values we have decided to enumerate.

This makes it impossible to select certain fonts (Roboto Thin for instance), when they have weights that fall too close to a font in the same family with a weight that is actually enumerated.

In Qt 6 we should fix the type to be an int, like in QFont. Hopefully this can be done in a fully source compatible way.