Fix handling of ampersands in wxCheckListBox under MSW

They were incorrectly interpreted as mnemonics when drawing
wxCheckListBox items, which didn't make sense and was inconsistent with
the other ports and even wxListBox in wxMSW itself.

It also affected wxRearrangeCtrl under MSW, which uses wxCheckListBox
for its implementation.

Closes #19201.

src/msw/checklst.cpp

@@ -100,6 +100,15 @@ public:
     void Toggle()
         { Check(!IsChecked()); }
 
+protected:
+    virtual int MSWGetTextType() const wxOVERRIDE
+    {
+        // Don't handle mnemonics in the label specially, they don't make sense
+        // for the listbox items that can't be activated from keyboard using
+        // them.
+        return DST_TEXT;
+    }
+
 private:
     wxCheckListBox *m_parent;
     bool m_checked;