CppTools/CppEditor: Rename the TestDocument classes

It was not helpful that we had four different classes with the same name.
Note that they look suspiciously similar and could possibly be merged
into a single class at some point.

Change-Id: I7d4c10a09408226037bc0d276940bca39dc5f576
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/cppeditor/cppquickfix_test.h

@@ -50,7 +50,7 @@ namespace Tests {
 /// reads the document.
 ///
 
-class QuickFixTestDocument : public TestDocument
+class QuickFixTestDocument : public GenericCppTestDocument
 {
 public:
     typedef QSharedPointer<QuickFixTestDocument> Ptr;