Merge CppTools into CppEditor

There was no proper separation of responsibilities between these
plugins. In particular, CppTools had lots of editor-related
functionality, so it's not clear why it was separated out in the first
place.
In fact, for a lot of code, it seemed quite arbitrary where it was put
(just one example: switchHeaderSource() was in CppTools, wheras
switchDeclarationDefinition() was in CppEditor).
Merging the plugins will enable us to get rid of various convoluted
pseudo-abstractions that were only introduced to keep up the artificial
separation.

Change-Id: Iafc3bce625b4794f6d4aa03df6cddc7f2d26716a
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/qmljstools/qmljsmodelmanager.cpp

@@ -34,7 +34,7 @@
 #include <coreplugin/messagemanager.h>
 #include <coreplugin/progressmanager/progressmanager.h>
 
-#include <cpptools/cppmodelmanager.h>
+#include <cppeditor/cppmodelmanager.h>
 
 #include <projectexplorer/buildconfiguration.h>
 #include <projectexplorer/buildsystem.h>
@@ -207,10 +207,10 @@ ModelManager::~ModelManager() = default;
 
 void ModelManager::delayedInitialization()
 {
-    CppTools::CppModelManager *cppModelManager = CppTools::CppModelManager::instance();
+    CppEditor::CppModelManager *cppModelManager = CppEditor::CppModelManager::instance();
     // It's important to have a direct connection here so we can prevent
     // the source and AST of the cpp document being cleaned away.
-    connect(cppModelManager, &CppTools::CppModelManager::documentUpdated,
+    connect(cppModelManager, &CppEditor::CppModelManager::documentUpdated,
             this, &ModelManagerInterface::maybeQueueCppQmlTypeUpdate, Qt::DirectConnection);
 
     connect(SessionManager::instance(), &SessionManager::projectRemoved,