Proposal: AppWindow.LayoutDirection Property for RTL Language support

# Proposal: AppWindow.LayoutDirection Property for RTL Language support

AppWindow.LayoutDirection 属性——支持 RTL 语言
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## Summary

在一些国家和地区的语言中，文字排列是从右到左的，这时候需要设置窗口扩展样式为 WS_EX_LAYOUTRTL，希望 AppWindow 能加入 LayoutDirection 属性，能设置窗口这个样式
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In some countries and regions of the language, text is arranged from right to left, this time you need to set the window extension style to WS_EX_LAYOUTRTL, hope AppWindow can add the LayoutDirection property, can set the window this style

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Existing code (已有代码)


https://github.com/microsoft/microsoft-ui-xaml/blob/d74a0332cf0d5e58f12eddce1070fa7a79b4c2db/src/dxaml/xcp/components/WindowChrome/WindowHelpers.cpp#L176

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## Rationale

* {First reason for why we should consider this proposal}
* {Second reason for why we should consider this proposal}
* {etc}

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## Scope

| Capability | Priority |
| :---------- | :------- |
| This proposal will allow developers to accomplish W | Must |
| This proposal will allow end users to accomplish X | Should |
| This proposal will allow developers to accomplish Y | Could |
| This proposal will allow end users to accomplish Z | Won't |

## Important Notes

None

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## Open Questions

None

Start by reading the existing WS_EX_LAYOUTRTL handling in src/dxaml/xcp/components/WindowChrome/WindowHelpers.cpp around line 176, then review the linked WinUI feature proposal process. Done would require a decided AppWindow API proposal with defined scope and behavior, but the current issue leaves those sections as template placeholders.

Written by the indexing model from the issue text.