Add wxThread::MSWGetHandle().

Under MSW a thread has both an ID, returned by wxThread::GetId(), and a
handle, which couldn't be retrieved so far. Add an accessor to do it.

Closes #16170.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76418 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/thread.h

@@ -1107,6 +1107,15 @@ public:
     */
     wxThreadIdType GetId() const;
 
+    /**
+        Gets the native thread handle.
+
+        This method only exists in wxMSW, use GetId() in portable code.
+
+        @since 3.1.0
+    */
+    WXHANDLE MSWGetHandle() const;
+
     /**
         Returns the thread kind as it was given in the ctor.