Utils: Avoid intermediate widgets when using LayoutBuilder

In most cases, the layout constructed in the builder was set
on a widget which in turn was put into a vbox in the actual
widget. This is not necessary, but needs some re-ordering.

Also make sure that using not-yet-parented widgets during
layout construction does not cause visible artifacts.

Change-Id: I75727a571da093d3131ea6fba467c2c646cdb6f1
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/projectexplorer/buildconfiguration.cpp

@@ -326,11 +326,12 @@ NamedWidget *BuildConfiguration::createConfigWidget()
         widget = named;
     }
 
-    LayoutBuilder builder(widget);
+    Layouting::Form builder;
     for (BaseAspect *aspect : aspects()) {
         if (aspect->isVisible())
             aspect->addToLayout(builder.finishRow());
     }
+    builder.attachTo(widget, false);
 
     return named;
 }