Expand the method that InputKeyboardSource can be obtained through HWND

[Gaoyifei1011]

Expand the method that InputKeyboardSource can be obtained through HWND
请扩展 InputKeyboardSource 可以通过窗口 HWND 获取的方法

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At present, InputKeyboardSource class can only be obtained by ContentIsland method, which means that this class can only be used in WinUI 3 framework. However, most methods of this class are applicable to other non-WinUI 3 Windows, so I hope to extend this class. Add InputKeyboardSource. GetForWindowId () method, using InputKeyboardSource allow other window.
目前 InputKeyboardSource 类只能通过 ContentIsland 方法获取，这也就是说，该类仅能在 WinUI 3 框架中使用，然而该类的大部分方法适用于其他非 WinUI 3 窗口，所以希望能扩展该类，添加 InputKeyboardSource.GetForWindowId() 方法，允许其他窗口使用 InputKeyboardSource。

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Reference links（参考链接）
https://learn.microsoft.com/windows/windows-app-sdk/api/winrt/microsoft.ui.input.inputkeyboardsource?view=windows-app-sdk-1.6