Drag-and-Drop Event and Visual State Issues with TreeViewItem in WinUI 3

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### Describe the bug

There have been two issues found while using the drag-and-drop feature with `TreeViewItem`:

### 'DragOver' and 'Drop' Events Not Triggered
When dragging an element from a different component onto a `TreeViewItem`, the `DragOver` and `Drop` events are not triggered if the item is hovered over or dropped **directly** without interacting with other items first. However, if multiple items are hovered over sequentially, the events fire as expected, starting from the second item onward.

**UPDATE**: The proposed workaround for this issue was to use the `DragEnter` event instead, which does work. However, I still find it inconsistent that two similar events get triggered differently. Moreover, `DragOver` is the only event handler that is proposed to accept the request in this article, which seems a bit confusing: https://learn.microsoft.com/en-us/windows/apps/design/input/drag-and-drop

### Stuck 'PointerOver' Visual State
Dragging an element from a different component and dropping it onto a `TreeViewItem` causes the item to remain stuck in the `PointerOver` visual state forever, unless it gets touched with another dragged item again.

The workaround for the 2nd issue by using `VisualStateManager.GoToState` **has issues as well**. Although it can force the visual state to revert to `Normal`, this only works if the state was set **after** the pointer left the item. If it was set while the pointer was on the item, the item will revert to its wrong `PointerOver` state again as soon as the pointer is out. To fully resolve the issue, the `VisualStateManager.GoToState` has to be put inside the `PointerExit` event handler.

### Steps to reproduce the bug

1. Run the project: https://github.com/datskiy/TreeViewItemDropIssue
2. Drag the pink square and hover over or drop it **directly** onto any `TreeViewItem`, without touching any other items.
3. Observe that the `DragOver` and `Drop` events **are not triggered** unless you hover over multiple items first. The drop will fire the `DragLeave` event only.
4. Drop the element onto a `TreeViewItem` and observe that the chosen `TreeViewItem` item gets **stuck** in the `PointerOver` state.

### Expected behavior

- `DragOver` and `Drop` events should consistently trigger when interacting with `TreeViewItem`.
- `TreeViewItem` should properly transition out of the `PointerOver` visual state after a drop operation.

### Screenshots

_No response_

### NuGet package version

WinUI 3 - Windows App SDK 1.6.3: 1.6.241114003

### Windows version

Windows 11 (24H2): Build 26100

### Additional context

The `VisualStateManager` workaround mentioned above might help with the stuck `PointerOver` state, but only when the pointer exited the item.

Source code: https://github.com/datskiy/TreeViewItemDropIssue

Start by running the linked TreeViewItemDropIssue reproduction project with Windows App SDK 1.6.3 and observe the DragOver, Drop, DragLeave, and PointerOver behavior. Then inspect the TreeViewItem drag-and-drop event handling and visual-state transitions; done means direct drops consistently raise the expected events and the item leaves PointerOver after the operation.

Written by the indexing model from the issue text.