CppEditor: Extend "Add Include" quickfix

... so it works for all kinds of symbols, not just Qt classes.

Fixes: QTCREATORBUG-21
Change-Id: I2d329c09b64cd8f7eef8cce7d9f022aca8586c0d
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/cppeditor/cppquickfixes.h

@@ -67,6 +67,8 @@ public:
                                        const QString &include);
     void perform() override;
 
+    QString include() const { return m_include; }
+
 private:
     QString m_include;
 };