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/window.h

@@ -586,6 +586,10 @@ public:
     // Should be overridden by all classes storing the "last focused" window.
     virtual void WXDoUpdatePendingFocus(wxWindow* WXUNUSED(win)) {}
 
+    // Called from WM_DPICHANGED handler for all windows to let them update
+    // any sizes and fonts used internally when the DPI changes.
+    void MSWUpdateOnDPIChange(const wxSize& oldDPI, const wxSize& newDPI);
+
 protected:
     // this allows you to implement standard control borders without
     // repeating the code in different classes that are not derived from