IndicatorView: Fix MaximumVisible not respected when using custom IndicatorTemplate (#31469)

<!-- Please let the below note in for people that find this PR -->
> [!NOTE]
> Are you waiting for the changes in this PR to be merged?
> It would be very helpful if you could [test the resulting
artifacts](https://github.com/dotnet/maui/wiki/Testing-PR-Builds) from
this PR and let us know in a comment if this change resolves your issue.
Thank you!

### Issue Details

- When using IndicatorView with a custom IndicatorTemplate, the
MaximumVisible property is not respected.

### Root Cause
- When IndicatorView uses a custom IndicatorTemplate, the BindableLayout
path is used to render indicators. In
IndicatorStackLayout.BindIndicatorItems(), the full ItemsSource was
passed directly to BindableLayout.SetItemsSource() without applying the
MaximumVisible limit.
- The MaximumVisible cap was only enforced in the native (non-template)
code path.

### Description of Change
- Modified BindIndicatorItems() in IndicatorStackLayout to call a new
GetFilteredItemsSource() helper before binding. The helper returns a
filtered List<object> capped at MaximumVisible items when the source has
more items than the limit; otherwise, it returns the original
ItemsSource unchanged.
- This fix applies on both initial render and when MaximumVisible
changes dynamically, because
IndicatorView.MaximumVisibleProperty.propertyChanged calls
ResetIndicators() → BindIndicatorItems().

### Key Technical Details
**IndicatorStackLayout.GetFilteredItemsSource():**

1. Returns null if ItemsSource is null or MaximumVisible <= 0
2. Returns the original ItemsSource if totalCount <= MaximumVisible (no
filtering needed)
3. Otherwise enumerates up to MaximumVisible items into a new list of
objects and returns it.

**Code path (with IndicatorTemplate):**
BindIndicatorItems() → GetFilteredItemsSource() →
BindableLayout.SetItemsSource(filtered)



**Code path (without IndicatorTemplate):**
Not affected — native rendering handles MaximumVisible separately.

### Issues Fixed
Fixes #31145 

### Validated the behaviour in the following platforms

- [x] Windows
- [x] Android
- [x] iOS
- [x] Mac

### Output
| Platform | Before Fix | After Fix |
|----------|----------|----------|
| Android | <video
src="https://github.com/user-attachments/assets/b077642e-d634-42a3-8d61-8374ac599b43">
| <video
src="https://github.com/user-attachments/assets/cd4b29b1-4087-41cc-a7f3-67396accfe6b">
|
| iOS | <video
src="https://github.com/user-attachments/assets/297cfde8-bffe-4fcb-a08b-a43362c944ff">
| <video
src="https://github.com/user-attachments/assets/8062d14e-ba38-4015-83dd-ca01e218ebfd">
|
| Windows | <video
src="https://github.com/user-attachments/assets/69aad00d-1f51-47fc-b92f-a8b4fe2741ac">
| <video
src="https://github.com/user-attachments/assets/73eacf53-7d6d-4e87-a606-558ba3482158">
|
| Mac | <video
src="https://github.com/user-attachments/assets/49720bbc-ce67-49d6-95a0-6a8018b5d4fa">
| <video
src="https://github.com/user-attachments/assets/8e494e0c-c795-4b62-894a-ddfdc4e4c27b">
|

Author: SyedAbdulAzeemSF4852

src/Controls/src/Core/IndicatorView/IndicatorStackLayout.cs

@@ -1,4 +1,8 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
 using System.ComponentModel;
+using System.Linq;
 using Microsoft.Maui.Controls.Shapes;
 using Microsoft.Maui.Graphics;
 
@@ -161,10 +165,44 @@ void BindIndicatorItems()
 				}
 			});
 
-			BindableLayout.SetItemsSource(this, _indicatorView.ItemsSource);
+			// Get the filtered items source based on MaximumVisible
+			var itemsSource = GetFilteredItemsSource();
+			BindableLayout.SetItemsSource(this, itemsSource);
+
 			BindableLayout.SetItemTemplate(this, indicatorTemplate);
 		}
 
+		IEnumerable? GetFilteredItemsSource()
+		{
+			if (_indicatorView.ItemsSource is null || _indicatorView.MaximumVisible <= 0)
+			{
+				return null;
+			}
+
+			var itemsSource = _indicatorView.ItemsSource;
+			int totalCount = itemsSource is ICollection col
+				? col.Count
+				: itemsSource.Cast<object>().Count();
+
+			if (totalCount <= _indicatorView.MaximumVisible)
+			{
+				return itemsSource;
+			}
+
+			var filteredItems = new List<object>(_indicatorView.MaximumVisible);
+			foreach (var item in itemsSource)
+			{
+				if (filteredItems.Count >= _indicatorView.MaximumVisible)
+				{
+					break;
+				}
+
+				filteredItems.Add(item);
+			}
+
+			return filteredItems;
+		}
+
 		public void Remove()
 		{
 			_indicatorView.PropertyChanged -= IndicatorViewPropertyChanged;

src/Controls/tests/TestCases.Android.Tests/snapshots/android/VerifyIndicatorViewMaximumVisibleWithTemplate.png

@@ -0,0 +1,57 @@
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 31145, "MaximumVisible Property Not Working with IndicatorTemplate in IndicatorView", PlatformAffected.All)]
+public class Issue31145 : ContentPage
+{
+	public Issue31145()
+	{
+		Label descriptionLabel = new Label
+		{
+			Text = "The test passes if the IndicatorView with an IndicatorTemplate respects the MaximumVisible property; otherwise, it fails.",
+			FontSize = 18,
+			HorizontalOptions = LayoutOptions.Center,
+		};
+
+		IndicatorView indicatorView = new IndicatorView
+		{
+			ItemsSource = new List<string> { "Item1", "Item2", "Item3", "Item4", "Item5" },
+			IndicatorColor = Colors.Yellow,
+			SelectedIndicatorColor = Colors.Gray,
+			HorizontalOptions = LayoutOptions.Center
+		};
+
+		indicatorView.IndicatorTemplate = new DataTemplate(() =>
+		{
+			return new BoxView
+			{
+				WidthRequest = 10,
+				HeightRequest = 10,
+				HorizontalOptions = LayoutOptions.Center,
+				VerticalOptions = LayoutOptions.Center
+			};
+		});
+
+		Button updateMaximumVisibleBtn = new Button
+		{
+			AutomationId = "UpdateMaximumVisibleBtn",
+			Text = "Set MaximumVisible Property to 2"
+		};
+
+		updateMaximumVisibleBtn.Clicked += (s, e) =>
+		{
+			indicatorView.MaximumVisible = 2;
+		};
+
+		Content = new StackLayout
+		{
+			Padding = 20,
+			Spacing = 20,
+			Children =
+			{
+				descriptionLabel,
+				indicatorView,
+				updateMaximumVisibleBtn
+			}
+		};
+	}
+}

src/Controls/tests/TestCases.HostApp/Issues/Issue31145.cs

@@ -0,0 +1,23 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue31145 : _IssuesUITest
+{
+	public Issue31145(TestDevice device) : base(device)
+	{
+	}
+
+	public override string Issue => "MaximumVisible Property Not Working with IndicatorTemplate in IndicatorView";
+
+	[Test]
+	[Category(UITestCategories.IndicatorView)]
+	public void VerifyIndicatorViewMaximumVisibleWithTemplate()
+	{
+		App.WaitForElement("UpdateMaximumVisibleBtn");
+		App.Tap("UpdateMaximumVisibleBtn");
+		VerifyScreenshot();
+	}
+}