Rewrote wxMSW radio menu items code to support not only appending them.

Previously the radio menu items could only be appended to a menu in wxMSW,
inserting them (either in an existing radio group or to start a new one) not
only didn't work but could even result in crashes because invalid iterators in
the menu items list could be used.

Fix this by storing the ranges of all radio groups in wxMenu itself instead of
storing the information about the radio group an item belongs to in the item
itself and by updating this data whenever a new radio item is inserted. Also
get rid of the notion of "current radio group" in wxMenu which doesn't really
make any sense.

Finally add a unit test checking that inserting radio items works as expected.

Closes #13200.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67720 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/menuitem.h

@@ -61,11 +61,6 @@ public:
     // Win32 API
     WXWPARAM GetMSWId() const;
 
-    // mark item as belonging to the given radio group
-    void SetAsRadioGroupStart();
-    void SetRadioGroupStart(int start);
-    void SetRadioGroupEnd(int end);
-
 #if WXWIN_COMPATIBILITY_2_8
     // compatibility only, don't use in new code
     wxDEPRECATED(
@@ -130,18 +125,6 @@ private:
     // common part of all ctors
     void Init();
 
-    // the positions of the first and last items of the radio group this item
-    // belongs to or -1: start is the radio group start and is valid for all
-    // but first radio group items (m_isRadioGroupStart == false), end is valid
-    // only for the first one
-    union
-    {
-        int start;
-        int end;
-    } m_radioGroup;
-
-    // does this item start a radio group?
-    bool m_isRadioGroupStart;
 
 #if wxUSE_OWNER_DRAWN
     // item bitmaps