Merge pull request #30 from dotnet-campus/t/lindexi/FixStylusPlugInOrder_Internal

Fix StylusPlugIn OnStylusDown/Move/Up invoked on UI thread and called out of order

Author: kkwpsv

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/Stylus/Wisp/PenContexts.cs

@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
@@ -512,7 +512,7 @@ internal StylusPlugInCollection TargetPlugInCollection(RawStylusInputReport inpu
                 ptTablet = ptTablet * stylusDevice.TabletDevice.TabletDeviceImpl.TabletToScreen;
                 ptTablet.X = (int)Math.Round(ptTablet.X); // Make sure we snap to whole window pixels.
                 ptTablet.Y = (int)Math.Round(ptTablet.Y);
-                ptTablet = _stylusLogic.MeasureUnitsFromDeviceUnits(stylusDevice.CriticalActiveSource, ptTablet); // change to measured units now.
+                ptTablet = _stylusLogic.MeasureUnitsFromDeviceUnits(inputReport.InputSource ?? stylusDevice.CriticalActiveSource, ptTablet); // change to measured units now.
 
                 pic = HittestPlugInCollection(ptTablet); // Use cached rectangles for UIElements.
             }