Fix compilation error: Change InvalidateMeasure return type from void to bool

The IPlatformMeasureInvalidationController interface requires InvalidateMeasure to return bool, not void.

Returns false to stop propagation since we're handling the resize directly by recalculating size and updating the frame.

Author: kubaflo

src/Controls/src/Core/Compatibility/Handlers/Shell/iOS/ShellFlyoutHeaderContainer.cs

@@ -37,10 +37,11 @@ public override Thickness Margin
 
 		void IPlatformMeasureInvalidationController.InvalidateAncestorsMeasuresWhenMovedToWindow() { }
 
-		void IPlatformMeasureInvalidationController.InvalidateMeasure(bool isPropagating)
+		bool IPlatformMeasureInvalidationController.InvalidateMeasure(bool isPropagating)
 		{
 			var size = SizeThatFits(new CGSize(Superview.Frame.Width, double.PositiveInfinity));
 			Frame = new CGRect(Frame.X, Frame.Y, size.Width, size.Height);
+		return false;
 		}
 
 		public override void LayoutSubviews()