feat(iOS): Address rule CA1822

src/iOS/Avalonia.iOS/CombinedSpan3.cs

@@ -16,7 +16,7 @@ internal ref struct CombinedSpan3<T>
 
     public int Length => Span1.Length + Span2.Length + Span3.Length;
 
-    void CopyFromSpan(ReadOnlySpan<T> from, int offset, ref Span<T> to)
+    static void CopyFromSpan(ReadOnlySpan<T> from, int offset, ref Span<T> to)
     {
         if(to.Length == 0)
             return;

src/iOS/Avalonia.iOS/TouchHandler.cs

@@ -19,7 +19,7 @@ namespace Avalonia.iOS
             _tl = tl;
         }
 
-        ulong Ts(UIEvent evt) => (ulong) (evt.Timestamp * 1000);
+        static ulong Ts(UIEvent evt) => (ulong) (evt.Timestamp * 1000);
         private IInputRoot Root => _view.InputRoot;
         private static long _nextTouchPointId = 1;
         private Dictionary<UITouch, long> _knownTouches = new Dictionary<UITouch, long>();