ProjectExplorer: Prepare more flexibility to aspect layouting

This hides the explicit use of a QFormLayout from the aspect
interface in a new LayoutBuilder class. That currently works
only on a QFormLayout in the back, but opens the possibility
to use e.g. a QGridLayout as use on the Kits and some option
pages.

The aspects now only announce sub-widgets they like to add,
actuall positioning is does by a new LayoutBuilder class,
also cramming several widgets in an hbox in the right column
of the QFormLayout is done there.

Change-Id: I2b788192c465f2ab82261849d34e514697c5a491
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/android/androidrunconfiguration.h

@@ -43,7 +43,7 @@ public:
                                   Core::Id id = Core::Id());
     ~BaseStringListAspect() override;
 
-    void addToConfigurationLayout(QFormLayout *layout) override;
+    void addToLayout(ProjectExplorer::LayoutBuilder &builder) override;
 
     QStringList value() const;
     void setValue(const QStringList &val);