Bug 1652259 - Update client margins when DPI changes r=aklotz

Currently margin values only change when the window goes fullscreen, causes unexpected white borders when moving to a lower-DPI display. This patch fixes that by updating the values whenever DPI changes.

Differential Revision: https://phabricator.services.mozilla.com/D89493

widget/windows/nsWindow.cpp

@@ -7549,6 +7549,7 @@ void nsWindow::OnDPIChanged(int32_t x, int32_t y, int32_t width,
 
     Resize(x, y, width, height, true);
   }
+  UpdateNonClientMargins();
   ChangedDPI();
   ResetLayout();
 }