[Android] CollectionView: Defer RemainingItemsThresholdReached to avoid RecyclerView scroll callback warnings (#30907)

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### Root Cause

When `RemainingItemsThreshold` is met during a scroll, `OnScrolled`
calls `SendRemainingItemsThresholdReached()` synchronously. This
triggers `notifyItemRangeChanged` on the RecyclerView adapter while
still inside the scroll callback. RecyclerView asserts against adapter
modifications during layout/scroll passes, producing:

```
W/RecyclerView: Cannot call this method in a scroll callback. Scroll callbacks might be run during a measure & layout pass where you cannot change the RecyclerView data.
java.lang.IllegalStateException: ...RecyclerView.assertNotInLayoutOrScroll
```

This affects any scenario where `RemainingItemsThresholdReachedCommand`
(or the `RemainingItemsThresholdReached` event) modifies the bound
collection — including the common pattern of clearing and reloading
items followed by `ScrollTo(0)`.

### Description of Change

Defers `SendRemainingItemsThresholdReached()` until the RecyclerView
transitions to `ScrollStateIdle`, which is a guaranteed safe point
outside any layout/scroll callback.

**Changes in `RecyclerViewScrollListener.cs`:**
- Added `_pendingRemainingItemsThresholdReached` boolean field
- Replaced direct calls to
`_itemsView.SendRemainingItemsThresholdReached()` in `OnScrolled` with
calls to `HandleRemainingItemsThresholdReached()`
- Added private `HandleRemainingItemsThresholdReached()` method that
sets the pending flag
- Added `OnScrollStateChanged` override that fires the deferred event
when `newState == RecyclerView.ScrollStateIdle`, with disposal and null
guards
- Clears the pending flag in `Dispose(bool)` to avoid stale state

**Why `OnScrollStateChanged` / `ScrollStateIdle` instead of `Post()`:**

`recyclerView.Post()` posts to the next Looper tick, which can still be
a layout pass and trigger the same RecyclerView assertion. Using
`ScrollStateIdle` is a stronger guarantee — it signals that RecyclerView
has fully settled and adapter mutations are safe.

### What NOT to Do (for future agents)

- ❌ **Don't call `SendRemainingItemsThresholdReached()` directly in
`OnScrolled`** — RecyclerView
asserts against adapter modifications during scroll/layout passes; this
causes
  `IllegalStateException` warnings.
- ❌ **Don't use `recyclerView.Post()`** — `Post()` only defers to the
next Looper tick, which
may still be a layout pass and can trigger the same RecyclerView
assertion. `ScrollStateIdle`
  is a stronger, safer guarantee.

### Issues Fixed

Fixes #23030
Fixes #25010

### Platforms Tested

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

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### Output
| Before| After|
|--|--|
| <video
src="https://github.com/user-attachments/assets/80c204ed-1657-4303-85de-df3ba998237a">
| <video
src="https://github.com/user-attachments/assets/fc748a87-8419-4fa4-9286-7ba3999b6c97">
|

---------
Co-authored-by: Jakub Florkowski <kubaflo123@gmail.com>

Author: NirmalKumarYuvaraj

src/Controls/src/Core/Handlers/Items/Android/RecyclerViewScrollListener.cs

@@ -11,6 +11,7 @@ public class RecyclerViewScrollListener<TItemsView, TItemsViewSource> : Recycler
 		bool _disposed;
 		int _horizontalOffset, _verticalOffset;
 		TItemsView _itemsView;
+		bool _pendingRemainingItemsThresholdReached;
 		readonly bool _getCenteredItemOnXAndY = false;
 		bool _hasCompletedFirstLayout = false;
 
@@ -91,10 +92,34 @@ public override void OnScrolled(RecyclerView recyclerView, int dx, int dy)
 
 			if (isThresholdReached)
 			{
-				_itemsView.SendRemainingItemsThresholdReached();
+				HandleRemainingItemsThresholdReached();
 			}
 		}
 
+		public override void OnScrollStateChanged(RecyclerView recyclerView, int newState)
+		{
+			base.OnScrollStateChanged(recyclerView, newState);
+
+			// If we have a pending threshold reached event and the RecyclerView is now idle,
+			// it's safe to trigger the event without the risk of modifying the adapter during a scroll callback
+			if (_pendingRemainingItemsThresholdReached && newState == RecyclerView.ScrollStateIdle)
+			{
+				_pendingRemainingItemsThresholdReached = false;
+				if (!_disposed && _itemsView is not null)
+				{
+					_itemsView.SendRemainingItemsThresholdReached();
+				}
+			}
+		}
+
+		void HandleRemainingItemsThresholdReached()
+		{
+			// Mark that we need to trigger the threshold reached event
+			// This will be handled when the RecyclerView transitions to idle state
+			// to avoid the "Cannot call this method in a scroll callback" exception
+			_pendingRemainingItemsThresholdReached = true;
+		}
+
 		protected virtual (int First, int Center, int Last) GetVisibleItemsIndex(RecyclerView recyclerView)
 		{
 			var firstVisibleItemIndex = -1;
@@ -176,6 +201,7 @@ protected override void Dispose(bool disposing)
 			{
 				_itemsView = null;
 				ItemsViewAdapter = null;
+				_pendingRemainingItemsThresholdReached = false;
 			}
 
 			_disposed = true;

src/Controls/src/Core/PublicAPI/net-android/PublicAPI.Unshipped.txt

@@ -6,4 +6,5 @@
 override Microsoft.Maui.Controls.Shapes.Shape.OnPropertyChanged(string? propertyName = null) -> void
 ~override Microsoft.Maui.Controls.Handlers.Items.MauiRecyclerView<TItemsView, TAdapter, TItemsViewSource>.OnInterceptTouchEvent(Android.Views.MotionEvent e) -> bool
 ~override Microsoft.Maui.Controls.Handlers.Items.MauiRecyclerView<TItemsView, TAdapter, TItemsViewSource>.OnTouchEvent(Android.Views.MotionEvent e) -> bool
-~override Microsoft.Maui.Controls.Handlers.Items.SelectableItemsViewAdapter<TItemsView, TItemsSource>.IsSelectionEnabled(Android.Views.ViewGroup parent, int viewType) -> bool
+~override Microsoft.Maui.Controls.Handlers.Items.RecyclerViewScrollListener<TItemsView, TItemsViewSource>.OnScrollStateChanged(AndroidX.RecyclerView.Widget.RecyclerView recyclerView, int newState) -> void
+~override Microsoft.Maui.Controls.Handlers.Items.SelectableItemsViewAdapter<TItemsView, TItemsSource>.IsSelectionEnabled(Android.Views.ViewGroup parent, int viewType) -> bool