ViewHandler: Skip null ToolTip initialization (#37842)

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## Description

Skips the platform ToolTip update while a new handler is connecting when
the virtual view has the default `null` ToolTip.

Reconnects still execute the update so a reused platform view can clear
stale state. Dynamic non-null and null updates are unchanged.

## Benchmark

The local Sandbox harness is not included in this PR. Release iOS
simulator, iPhone 16 Pro / iOS 18.4:

| Metric | Result |
|---|---:|
| Heavy tile `ToPlatform` (55 elements) | 12.771 ms |
| Flat tile `ToPlatform` (14 elements) | 4.844 ms |
| ToolTip mapper activity, 480 initial handlers | 0.236 ms |

The mapper activity count remains 480 because attribution wraps the
mapper entry even when the new guard returns immediately. This
micro-optimization is below end-to-end simulator noise and no aggregate
speedup is claimed. The run completed all 70 benchmark results with
`run-end|ok`.

## Review

Independent GPT, Claude, and Gemini reviews traced connection,
reconnect, null/default values, dynamic updates, custom implementations,
and all platform paths. All three found the guard safe and consistent
with existing connect-time mapper guards.

Copilot-Session: 5a03e13d-1a41-4652-a8c6-099eeb79cd50

Author: StephaneDelcroix

src/Core/src/Handlers/View/ViewHandler.cs

@@ -655,7 +655,14 @@ public static void MapToolTip(IViewHandler handler, IView view)
 		{
 #if PLATFORM
 			if (view is IToolTipElement tooltipContainer)
+			{
+				if (handler.IsConnectingHandler() && tooltipContainer.ToolTip is null)
+				{
+					return;
+				}
+
 				handler.ToPlatform().UpdateToolTip(tooltipContainer.ToolTip);
+			}
 #endif
 		}