feat(windows): disable pen tap / press-hold visual feedback

On pen-down the OS drew the "Windows Ink" tap ripple / press-and-hold ring
under the nib — ugly and laggy-looking while writing. Set the tablet input
service's MicrosoftTabletPenServiceProperty on both the top-level window and
the Flutter child (where WM_POINTER lands) with the disable flags
(PENTAPFEEDBACK, PRESSANDHOLD, PENBARRELFEEDBACK, TOUCHUIFORCEON/OFF, FLICKS)
so the pen draws instantly with no OS animation.

Native-only change (windows/runner/flutter_window.cpp); built by CI.

windows/runner/flutter_window.cpp

@@ -29,6 +29,32 @@ LRESULT CALLBACK FlutterChildSubclassProc(HWND hwnd, UINT message,
   return DefSubclassProc(hwnd, message, wparam, lparam);
 }
 
+// Turn off the OS-drawn pen visual feedback (the "Windows Ink" tap ripple, the
+// press-and-hold right-click ring, barrel feedback, and flicks) so the pen
+// draws instantly with no ugly OS animation under the nib. The tablet input
+// service reads these flags from a window property; set it on whichever window
+// receives the pointer input. Flag values are from the Windows pen/tablet docs
+// (not declared in the public SDK headers).
+void DisablePenVisualFeedback(HWND hwnd) {
+  if (!hwnd) {
+    return;
+  }
+  constexpr ULONG_PTR kDisablePressAndHold = 0x00000001;
+  constexpr ULONG_PTR kDisablePenTapFeedback = 0x00000008;
+  constexpr ULONG_PTR kDisablePenBarrelFeedback = 0x00000010;
+  constexpr ULONG_PTR kDisableTouchUIForceOn = 0x00000100;
+  constexpr ULONG_PTR kDisableTouchUIForceOff = 0x00000200;
+  constexpr ULONG_PTR kDisableFlicks = 0x00010000;
+  const ULONG_PTR flags = kDisablePressAndHold | kDisablePenTapFeedback |
+                          kDisablePenBarrelFeedback | kDisableTouchUIForceOn |
+                          kDisableTouchUIForceOff | kDisableFlicks;
+  const ATOM atom = ::GlobalAddAtomW(L"MicrosoftTabletPenServiceProperty");
+  if (atom != 0) {
+    ::SetPropW(hwnd, MAKEINTATOM(atom), reinterpret_cast<HANDLE>(flags));
+    ::GlobalDeleteAtom(atom);
+  }
+}
+
 }  // namespace
 
 FlutterWindow::FlutterWindow(const flutter::DartProject& project)
@@ -64,6 +90,11 @@ bool FlutterWindow::OnCreate() {
     SetWindowSubclass(flutter_child, FlutterChildSubclassProc, kPenSubclassId, 0);
   }
 
+  // Kill the OS pen tap/press-and-hold visual feedback on both the top-level
+  // window and the Flutter child (the one that actually gets the pointer input).
+  DisablePenVisualFeedback(GetHandle());
+  DisablePenVisualFeedback(flutter_child);
+
   flutter_controller_->engine()->SetNextFrameCallback([&]() {
     this->Show();
   });