[clang] [clang][doc]: Merge entries with duplicate content. (PR #134089)

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YLChenZ wrote:

> I'm still seeing `cf_returns_retained` that's distinct from `cf_returns_not_retained`, etc.

 @AaronBallman Really? But here's what I'm getting when I run it:

![屏幕截图 2025-04-07 195538](https://github.com/user-attachments/assets/a1a61b46-3fdb-4e58-adde-d35b7c9562fe)



https://github.com/llvm/llvm-project/pull/134089