move Capture(null) from Pointer.Dispose() to callsites (#21363)

Co-authored-by: Jan Kučera <miloush@users.noreply.github.com>

src/Avalonia.Base/Input/PenDevice.cs

@@ -104,7 +104,7 @@ namespace Avalonia.Input
 
             if (source != null)
             {
-                pointer.Capture(source);
+                pointer.Capture(source, CaptureSource.Implicit);
                 var settings = ((IInputRoot?)(source as Interactive)?.GetVisualRoot())?.PlatformSettings;
                 if (settings is not null)
                 {
@@ -173,7 +173,7 @@ namespace Avalonia.Input
                 }
                 finally
                 {
-                    pointer.Capture(null);
+                    pointer.Capture(null, CaptureSource.Implicit);
                     pointer.CaptureGestureRecognizer(null);
                     pointer.IsGestureRecognitionSkipped = false;
                     _lastMouseDownButton = default;

src/Avalonia.Base/Input/Pointer.cs

@@ -136,10 +136,7 @@ namespace Avalonia.Input
 
         public void Dispose()
         {
-            if (Captured != null)
-            {
-                Capture(null);
-            }
+            // callers are responsible for calling Capture(null, source) with an appropriate source
         }
 
         /// <summary>

src/Avalonia.Base/Input/TouchDevice.cs

@@ -48,7 +48,7 @@ namespace Avalonia.Input
 
                 _pointers[args.RawPointerId] = pointer = new Pointer(Pointer.GetNextFreeId(),
                     PointerType.Touch, _pointers.Count == 0);
-                pointer.Capture(hit);
+                pointer.Capture(hit, CaptureSource.Implicit);
             }
 
             var target = pointer.Captured ?? args.InputHitTestResult.firstEnabledAncestor ?? args.Root;
@@ -109,6 +109,7 @@ namespace Avalonia.Input
                     {
                         target.RaiseEvent(e);
                     }
+                    pointer?.Capture(null, CaptureSource.Implicit);
                 }
             }
 
@@ -117,7 +118,7 @@ namespace Avalonia.Input
                 _pointers.Remove(args.RawPointerId);
                 using (pointer)
                 {
-                    pointer?.Capture(null);
+                    pointer?.Capture(null, CaptureSource.Platform);
                     pointer?.CaptureGestureRecognizer(null);
                     if (pointer != null)
                         pointer.IsGestureRecognitionSkipped = false;