chore: remove the manual ui test in favor of a runtime test

src/SamplesApp/UITests.Shared/UITests.Shared.projitems

@@ -1414,10 +1414,6 @@
       <SubType>Designer</SubType>
       <Generator>MSBuild:Compile</Generator>
     </Page>
-    <Page Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Controls\AutoSuggestBoxTests\AutoSuggestBox_PopupFocus.xaml">
-      <SubType>Designer</SubType>
-      <Generator>MSBuild:Compile</Generator>
-    </Page>
     <Page Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Controls\AutoSuggestBoxTests\AutoSuggestBox_Icons.xaml">
       <SubType>Designer</SubType>
       <Generator>MSBuild:Compile</Generator>
@@ -6562,9 +6558,6 @@
     <Compile Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Controls\AutoSuggestBoxTests\AutoSuggestBox_Description.xaml.cs">
       <DependentUpon>AutoSuggestBox_Description.xaml</DependentUpon>
     </Compile>
-    <Compile Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Controls\AutoSuggestBoxTests\AutoSuggestBox_PopupFocus.xaml.cs">
-      <DependentUpon>AutoSuggestBox_PopupFocus.xaml</DependentUpon>
-    </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Controls\AutoSuggestBoxTests\AutoSuggestBox_Icons.xaml.cs">
       <DependentUpon>AutoSuggestBox_Icons.xaml</DependentUpon>
     </Compile>

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Controls/Given_TextBox.cs

@@ -28,6 +28,7 @@
 using Windows.UI.Input.Preview.Injection;
 using Windows.Foundation;
 using System.Collections.Generic;
+using Uno.Extensions;
 
 
 #if WINAPPSDK
@@ -1124,6 +1125,44 @@ static FrameworkElement GetSCP(TextBox tb)
 		}
 #endif
 
+#if HAS_UNO
+		[TestMethod]
+		[UnoWorkItem("https://github.com/unoplatform/uno/issues/18790")]
+#if !HAS_INPUT_INJECTOR
+		[Ignore("InputInjector is not supported on this platform.")]
+#endif
+		public async Task When_Clicked_In_Popup()
+		{
+			TextBox tb;
+			var btn = new Button
+			{
+				Flyout = new Flyout
+				{
+					Content = tb = new TextBox()
+				}
+			};
+
+			await UITestHelper.Load(btn);
+
+			var injector = InputInjector.TryCreate() ?? throw new InvalidOperationException("Failed to init the InputInjector");
+			using var mouse = injector.GetMouse();
+
+			mouse.Press(btn.GetAbsoluteBoundsRect().GetCenter());
+			await UITestHelper.WaitForIdle();
+			mouse.Release();
+			await UITestHelper.WaitForIdle();
+
+			Assert.IsTrue(btn.Flyout.IsOpen);
+
+			mouse.Press(tb.GetAbsoluteBoundsRect().GetCenter());
+			await UITestHelper.WaitForIdle();
+			mouse.Release();
+			await UITestHelper.WaitForIdle();
+
+			Assert.AreEqual(tb, FocusManager.GetFocusedElement(WindowHelper.XamlRoot));
+		}
+#endif
+
 		private static async Task<TextBox> LoadZeroSizeTextBoxAsync(Style style)
 		{
 			var loaded = false;

src/Uno.UI/UI/Xaml/Controls/ScrollViewer/ScrollViewer.cs

@@ -593,17 +593,6 @@ public double HorizontalOffset
 			);
 		#endregion
 
-#if __WASM__
-		/// <summary>
-		/// This is specifically added for ScrollViewers inside TextBoxes and specifically for WASM
-		/// On WASM, a click on a TextBox inside a popup shifts focus to the Popup instead of the TextBox
-		/// as a result of ScrollContentControl_SetFocusOnFlyoutLightDismissPopupByPointer.
-		/// This is only a problem on WASM because we don't capture the pointer when pressing inside a TextBox
-		/// <seealso cref="TextBox.IsPointerCaptureRequired"/>.
-		/// </summary>
-		internal bool DisableSetFocusOnPopupByPointer { get; set; }
-#endif
-
 		private readonly SerialDisposable _sizeChangedSubscription = new SerialDisposable();
 
 #pragma warning disable 649 // unused member for Unit tests

src/Uno.UI/UI/Xaml/Controls/ScrollViewer/ScrollViewer.wasm.cs

@@ -11,6 +11,15 @@ namespace Microsoft.UI.Xaml.Controls
 {
 	partial class ScrollViewer
 	{
+		/// <summary>
+		/// This is specifically added for ScrollViewers inside TextBoxes and specifically for WASM
+		/// On WASM, a click on a TextBox inside a popup shifts focus to the Popup instead of the TextBox
+		/// as a result of ScrollContentControl_SetFocusOnFlyoutLightDismissPopupByPointer.
+		/// This is only a problem on WASM because we don't capture the pointer when pressing inside a TextBox
+		/// <seealso cref="TextBox.IsPointerCaptureRequired"/>.
+		/// </summary>
+		internal bool DisableSetFocusOnPopupByPointer { get; set; }
+
 		internal bool CancelNextNativeScroll { get; private set; }
 		internal Size ScrollBarSize => (_presenter as ScrollContentPresenter)?.ScrollBarSize ?? default;