Provide API to detect passive interactor areas of widgets

[4.4] QToolBar:
Add accessor for the handleRect() area of QToolBarLayout. <= fixed through subElementRect SE_ToolBarHandle

[4.5] Introduce methods (QStyle?) to tell in what kind of subarea/subcontrol a given point is in a QWidget:

We want a [computationally inexpensive] method to tell whether an area of a widget is a "Passive interactor" , that is, whether Designer should refrain from blocking events in that area (for example, a toolbar handle, scrollbar handle, etc). QUestion is, whether a simple bool is sufficient .. enumeration instead?

Look at tools/designer/src/lib/shared/widgetfactory.cpp:555 / bool WidgetFactory::isPassiveInteractor(QWidget *widget)
to get an idea.

Please look at the parent task as to why this makes sense. As of 8.2.2008, Designer will not be the LSB test app; still we would like to
get rid of _p.h