fix: Make Clipboard.GetContentAsync reliable

Previously we were executing the GetClipboardText method on UI thread which was unnecessary, and as it was executed asynchronously, it did not necessarily wait for the actual promise on JS side to finish executing. Therefore in most cases just the initial empty string content was returned.

src/Uno.UWP/ApplicationModel/DataTransfer/Clipboard.wasm.cs

@@ -6,6 +6,7 @@
 using Windows.UI.Core;
 using Uno.Extensions.Specialized;
 using Uno.Foundation;
+using System.Threading;
 
 namespace Windows.ApplicationModel.DataTransfer
 {
@@ -36,25 +37,15 @@ public static DataPackageView GetContent()
 		{
 			var dataPackage = new DataPackage();
 
-			dataPackage.SetDataProvider(
-				StandardDataFormats.Text,
-				async ct =>
-				{
-					var text = string.Empty;
-					await Uno.UI.Dispatching.CoreDispatcher.Main.RunAsync(
-						Uno.UI.Dispatching.CoreDispatcherPriority.High,
-						async _ => text = await GetClipboardText());
-
-					return text;
-				});
+			dataPackage.SetDataProvider(StandardDataFormats.Text, async ct => await GetClipboardText(ct));
 
 			return dataPackage.GetView();
 		}
 
-		private static async Task<string> GetClipboardText()
+		private static async Task<string> GetClipboardText(CancellationToken ct)
 		{
 			var command = $"{JsType}.getText();";
-			var text = await WebAssemblyRuntime.InvokeAsync(command);
+			var text = await WebAssemblyRuntime.InvokeAsync(command, ct);
 
 			return text;
 		}