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/clangtools/clangselectablefilesdialog.cpp

@@ -29,7 +29,7 @@
 
 #include <coreplugin/actionmanager/actionmanager.h>
 #include <coreplugin/find/itemviewfind.h>
-#include <cpptools/projectinfo.h>
+#include <cppeditor/projectinfo.h>
 #include <projectexplorer/selectablefilesmodel.h>
 #include <texteditor/textdocument.h>
 
@@ -41,7 +41,7 @@
 #include <QSortFilterProxyModel>
 #include <QStandardItem>
 
-using namespace CppTools;
+using namespace CppEditor;
 using namespace Utils;
 using namespace ProjectExplorer;