Correctly set up grouped properties in QQmlJSImportVisitor

To properly analyse code in the QML code model, we need to have proper support for grouped properties (which are required for important properties like anchors).

Currently, we don't set them up correctly in the QQmlJSScope tree.

Currently, we e.g. end up with an invalid binding on a nonexisting fill property when writing

Item {anchors.fill: parent}

instead of a binding to the Item's anchor property, and a binding to anchor's fill property.

Related: the TODO in 

bool QQmlJSImportVisitor::visit(UiScriptBinding *scriptBinding)

There are probably  other broken partsj