CppEditor: Deprecate "assign to local" quickfix

... in favor of clangd's "Extract Variable" tweak.
As of https://github.com/llvm/llvm-project/pull/112525, this
functionality should be fully covered by clangd.

Task-number: QTCREATORBUG-9363
Task-number: QTCREATORBUG-9578
Change-Id: I00ce996ef37b26152d93ed91fa5d1ea69e619618
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/cppeditor/quickfixes/assigntolocalvariable.cpp

@@ -123,8 +123,13 @@ private:
 //! Assigns the return value of a function call or a new expression to a local variable
 class AssignToLocalVariable : public CppQuickFixFactory
 {
-#ifdef WITH_TESTS
 public:
+    AssignToLocalVariable()
+    {
+        setClangdReplacement({20});
+    }
+
+#ifdef WITH_TESTS
     static QObject *createTest();
 #endif