Newer versions of Qt can evaluate expressions without pausing the
QML engine. We can take advantage of that. At the same time we can
remove the crutch of using QQmlEngineDebugService for this. The
latter produces inconsistent and generally worse results than the V4
debug service.

Task-number: QTCREATORBUG-14931
Change-Id: Ic78d08a0b00cf7de3911b7b672ce229c6d779363
Reviewed-by: hjk <hjk@theqtcompany.com>