Bug title: Please bring back ToolTip DesktopAcrylicBackdrop

### Describe the bug

Bug title: Please bring back ToolTip DesktopAcrylicBackdrop

请为工具提示带回 DesktopAcrylicBackdrop

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Currently, the default background color of WinUI 3 ToolTip is solid color, that is, the background color set with SolidColorBrush. However, in WinUI 2, the background color of ToolTip is acrylic background. It is hoped that in the future, acrylic background colors can be brought back to the ToolTip of WinUI 3

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目前默认的 WinUI 3 ToolTip 背景色是纯色，也就是用 SolidColorBrush 设置的背景色，但是在 WinUI 2 中，ToolTip 背景色是亚克力背景，希望未来能为 WinUI 3 的 ToolTip 带回亚克力背景色

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WinUI 3 With DesktopAcrylicBackdrop ToolTip

WinUI 3 default ToolTip

WinUI 2(UWP/Xaml islands) ToolTip

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临时解决方案
给 ToolTip 挂载 Loaded 事件，然后在 Loaded 事件中添加以下实现
```
private void OnLoaded(object sender, object args)
{
if(sender is ToolTip toolTip)
{
(toolTip.Parent as Popup).RequestedTheme = `ElementTheme.Default;
(toolTip.Parent as Popup).SystemBackdrop = new MaterialBackdrop(DesktopAcrylicKind.Default);
}
}
```

### Steps to reproduce the bug

See description

### Expected behavior

See description

### Screenshots

See description

### NuGet package version

WinUI 3 - Windows App SDK 1.7.3: 1.7.250606001

### Windows version

Windows 11 (24H2): Build 26100

### Additional context

See description

Start with the ToolTip and DesktopAcrylicBackdrop behavior described in the issue, comparing the WinUI 3 default and WinUI 2 screenshots and the Windows App SDK 1.7.3 environment. No files or tests are named; done means WinUI 3 ToolTip uses the expected acrylic background without the documented Loaded-event workaround.

Written by the indexing model from the issue text.