Add framework for Per-Monitor DPI Awareness on Windows

React to the WM_DPICHANGED event and update the size of the  child windows and
the top-level window. Scale the minimum and maximum window size to the new DPI.

Only react to WM_DPICHANGED when DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2 is
used.

include/wx/msw/missing.h

@@ -23,7 +23,11 @@
 #endif
 
 #ifndef WM_PRINTCLIENT
-    #define WM_PRINTCLIENT 0x318
+    #define WM_PRINTCLIENT      0x0318
+#endif
+
+#ifndef WM_DPICHANGED
+    #define WM_DPICHANGED       0x02E0
 #endif
 
 #ifndef DT_HIDEPREFIX