Apparently, it did not like ::label

When a change is done to an element that cannot be changed due to
debugger/qdeclarative limitations, a warning is shown to the user in QML
JS Editor.

Reviewed-by: Olivier Goffart

QmlJsDelta:  Fix the fact that sometimes, when inserting items, the new item could match the next item

Also used 'int' instead of QDeclarativeDebugObjectReference for
the debug id in order not to use the private API from QMLJS

Such as anchors and font.

This required a little bit of refactoring.
The Delta::update should now be faster.

The root is enough because the rest of the tree will be added as the
root is added

Else, the line numbers does not match anymore.

... with a little bit of refactoring.

But for some reason it does not seem to have an effect

Use a smarter way to compare the AST (based on the diffX algorithm)
That way we do not rely anymore on the id property