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>

tests/auto/cplusplus/codeformatter/tst_codeformatter.cpp

@@ -29,8 +29,8 @@
 #include <QTextDocument>
 #include <QTextBlock>
 
-#include <cpptools/cppcodeformatter.h>
-using namespace CppTools;
+#include <cppeditor/cppcodeformatter.h>
+using namespace CppEditor;
 
 class tst_CodeFormatter: public QObject
 {