Fix issue that breaking IME discards input buffer (#14433)

Co-authored-by: Benedikt Stebner <Gillibald@users.noreply.github.com>

src/Windows/Avalonia.Win32/Input/Imm32InputMethod.cs

@@ -334,11 +334,23 @@ namespace Avalonia.Win32.Input
             IsComposing = true;
         }
 
-        public void HandleCompositionEnd()
+        public void HandleCompositionEnd(uint timestamp)
         {
             //Cleanup composition state.
             IsComposing = false;
 
+            if (_parent != null && !string.IsNullOrEmpty(Composition))
+            {
+                var e = new RawTextInputEventArgs(WindowsKeyboardDevice.Instance, timestamp, _parent.Owner, Composition);
+
+                if (_parent.Input != null)
+                {
+                    _parent.Input(e);
+
+                    _parent._ignoreWmChar = true;
+                }
+            }
+
             Composition = null;
 
             if (IsActive)

src/Windows/Avalonia.Win32/WindowImpl.AppWndProc.cs

@@ -730,7 +730,7 @@ namespace Avalonia.Win32
                     }
                 case WindowsMessage.WM_IME_ENDCOMPOSITION:
                     {
-                        Imm32InputMethod.Current.HandleCompositionEnd();
+                        Imm32InputMethod.Current.HandleCompositionEnd(timestamp);
 
                         return IntPtr.Zero;
                     }