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/cmakeprojectmanager/cmakebuildconfiguration.cpp

@@ -185,10 +185,11 @@ CMakeBuildSettingsWidget::CMakeBuildSettingsWidget(CMakeBuildConfiguration *bc)
     });
     auto initialCMakeAspect = bc->aspect<InitialCMakeArgumentsAspect>();
     auto aspectWidget = new QWidget;
-    LayoutBuilder aspectWidgetBuilder(aspectWidget);
+    Layouting::Form aspectWidgetBuilder;
     buildDirAspect->addToLayout(aspectWidgetBuilder);
     aspectWidgetBuilder.finishRow();
     initialCMakeAspect->addToLayout(aspectWidgetBuilder);
+    aspectWidgetBuilder.attachTo(aspectWidget, false);
     mainLayout->addWidget(aspectWidget, row, 0, 1, -1);
     ++row;
 
@@ -196,9 +197,9 @@ CMakeBuildSettingsWidget::CMakeBuildSettingsWidget(CMakeBuildConfiguration *bc)
     connect(qmlDebugAspect, &QtSupport::QmlDebuggingAspect::changed, this, [this]() {
         updateButtonState();
     });
-    auto widget = new QWidget;
-    LayoutBuilder builder(widget);
+    Layouting::Form builder;
     qmlDebugAspect->addToLayout(builder);
+    auto widget = builder.emerge();
     mainLayout->addWidget(widget, row, 0, 1, -1);
 
     ++row;