QSequentiableIterable from a QVariant passed through QML loses valueMetaType info

When constructring a QSequentialIterable from a QVariant gotten from QML, the iterable valueMetaType is always QVariant.

Attached is an example demonstrating the issue (and showing the correct behavior with a QVariant that hasn't transited through QML).

The usecase is having a `QVariant` property that can be binded to any sequence (or associative) container and know the contained type (even with no element in the container) and iterate over the container.