Add a note for making ResultStoreBase's internal members private

There's no class inheriting from ResultStoreBase (and likely won't be),
so the destructor was marked to be made non-virtual in Qt 7. For the
same reason, the internal members don't need to be protected, and the
class shouldn't have "Base" in its name. Add a note about it.

Task-number: QTBUG-99883
Change-Id: I00d7a96d99d2c326d29bd421235a15d68b4d4e5c
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/corelib/thread/qresultstore.h

@@ -136,7 +136,8 @@ public:
     ResultIteratorBase resultAt(int index) const;
     bool contains(int index) const;
     int count() const;
-    // ### Qt 7: 'virtual' isn't required, can be removed
+    // ### Qt 7: 'virtual' isn't required, can be removed, along with renaming
+    // the class to ResultStore and changing the members below to be private.
     virtual ~ResultStoreBase();
 
 protected: