Utils/ProjectExplorer: Move re-usabled bits of aspects to Utils

Classes involved are BaseAspect and some derived classes,
LayoutBuilder and VariableChooser.

This is mostly mechanical, with various include/using changes
to make it compile.

Change-Id: I624a457f3555f102e541c4c71e33a9423af32250
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/qmlprojectmanager/qmlmainfileaspect.cpp

@@ -41,6 +41,8 @@
 
 #include <QComboBox>
 
+#include <utils/layoutbuilder.h>
+
 using namespace Core;
 using namespace ProjectExplorer;
 
@@ -69,7 +71,7 @@ QmlMainFileAspect::~QmlMainFileAspect()
     delete m_fileListCombo;
 }
 
-void QmlMainFileAspect::addToLayout(LayoutBuilder &builder)
+void QmlMainFileAspect::addToLayout(Utils::LayoutBuilder &builder)
 {
     QTC_ASSERT(!m_fileListCombo, delete m_fileListCombo);
     m_fileListCombo = new QComboBox;