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.

src/msw/window.cpp

@@ -4837,6 +4837,47 @@ wxSize wxWindowMSW::GetDPI() const
     return dpi;
 }
 
+// Helper function to update the given coordinate by the scaling factor if it
+// is set, i.e. different from wxDefaultCoord.
+static void ScaleCoordIfSet(int& coord, float scaleFactor)
+{
+    if ( coord != wxDefaultCoord )
+    {
+        const float coordScaled = coord * scaleFactor;
+        coord = scaleFactor > 1.0 ? ceil(coordScaled) : floor(coordScaled);
+    }
+}
+
+void
+wxWindowMSW::MSWUpdateOnDPIChange(const wxSize& oldDPI, const wxSize& newDPI)
+{
+    // update min and max size if necessary
+    const float scaleFactor = (float)newDPI.y / oldDPI.y;
+
+    ScaleCoordIfSet(m_minHeight, scaleFactor);
+    ScaleCoordIfSet(m_minWidth, scaleFactor);
+    ScaleCoordIfSet(m_maxHeight, scaleFactor);
+    ScaleCoordIfSet(m_maxWidth, scaleFactor);
+
+    InvalidateBestSize();
+
+    // update children
+    wxWindowList::compatibility_iterator current = GetChildren().GetFirst();
+    while ( current )
+    {
+        wxWindow *childWin = current->GetData();
+        // Update all children, except other top-level windows.
+        // These could be on a different monitor and will get their own
+        // dpi-changed event.
+        if ( childWin && !childWin->IsTopLevel() )
+        {
+            childWin->MSWUpdateOnDPIChange(oldDPI, newDPI);
+        }
+
+        current = current->GetNext();
+    }
+}
+
 // ---------------------------------------------------------------------------
 // colours and palettes
 // ---------------------------------------------------------------------------