CppEditor: Add quickfix for converting comments from C++ to C style

... and vice versa.

Fixes: QTCREATORBUG-27501
Change-Id: I8584cc1e86718b3fe0f0ead2a3436495303ca3c8
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/cppeditor/cpprefactoringchanges.h

@@ -12,6 +12,8 @@
 
 #include <texteditor/refactoringchanges.h>
 
+#include <optional>
+
 namespace CppEditor {
 
 class CppRefactoringChanges;
@@ -44,6 +46,8 @@ public:
 
     void startAndEndOf(unsigned index, int *start, int *end) const;
 
+    QList<CPlusPlus::Token> tokensForCursor() const;
+
     using TextEditor::RefactoringFile::textOf;
     QString textOf(const CPlusPlus::AST *ast) const;
 
@@ -55,6 +59,9 @@ protected:
     CppRefactoringChangesData *data() const;
     void fileChanged() override;
 
+    int tokenIndexForPosition(const std::vector<CPlusPlus::Token> &tokens, int pos,
+                              int startIndex) const;
+
     mutable CPlusPlus::Document::Ptr m_cppDocument;
 
     friend class CppRefactoringChanges; // for access to constructor