Improve the handling of multiple bindings to the same grouped property

It is possible to have multiple bindings to the same grouped property.

For example:

Text {
    font { pixelSize: 12 }
    font { pixelSize: 20 }
 

The engine doesn't issue any warning for this, compared to the general case where a property is bound multiple times albeit it is not necessarily clear what the value for `font.pixelSize` is intended to be.

In general, "We don't have any logic for consolidating the different QQmlJSScopes we get for grouped properties" .

This can, possibly, affect some of the tooling for QML, such as `qmllint`, when dealing with the cases such as the above one.

Improving might the handling of the multiple blocks for the same group property and generally providing some infrastructure for dealing with them can help improve the ability of the aforementioned tooling to add feature that interact with this for of grouped properties.