Please add SystemBackdrop property to TeachingTip

[Gaoyifei1011]

Describe the bug

Please add SystemBackdrop property to TeachingTip
希望能为 TeachingTip 控件带来 SystemBackdrop 属性

Most WinUI 3 controls can be set based on PopupRoot ShouldConstrainToRootBounds attribute and SystemBackdrop attribute, This means that these surfacing controls have their own control over where they are displayed and the Systembackdrop properties they use. In TeachingTip, however, we can only find ShouldConstrainToRootBounds attribute, cannot find SystemBackdrop attributes, when modifying TeachingTip background to transparent, TeachingTip is transparent because the SystemBackdrop property cannot be set. Hopefully, the SystemBackdrop property will be added to TeachingTip in the next release.
目前大部分 WinUI 3 基于 PopupRoot 的控件都可以自行设置 ShouldConstrainToRootBounds 属性和 SystemBackdrop 属性，这意味着这一部分浮出控件可以自行控制它们显示的位置和使用的背景色属性。然而，在 TeachingTip 中，我们只能找到 ShouldConstrainToRootBounds 属性，却找不到 SystemBackdrop 属性，当修改 TeachingTip 的背景为透明时，由于无法设置 SystemBackdrop 属性，故 TeachingTip 显示为透明，希望下一个版本中可以为 TeachingTip 带来 SystemBackdrop 属性

Steps to reproduce the bug

See describe

Expected behavior

When TeachingTip Background attribute is set to Transparent, ShouldConstrainToRootBounds when set to false, You can use the SystemBackdrop property to provide a system backdrop for the TeachingTip
当 TeachingTip Background 属性设置为 Transparent，ShouldConstrainToRootBounds 设置为 false时，通过设置 SystemBackdrop 属性可以为 TeachingTip 带来背景色

Screenshots

NuGet package version

WinUI 3 - Windows App SDK 1.5.1: 1.5.240311000

Windows version

Windows 11 (22H2): Build 22621

Additional context

No response