[clang] [clang][doc]: Merge the contents of identical entries. (PR #134089)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Thank you for working on this! I verified that it does address the issue with `randomize_layout` and `no_randomize_layout` being duplicated. But it doesn't seem to handle other cases like `cf_returns_not_retained`, `cf_returns_retained`, and `cf_consumed`, or `coro_return_type` and `coro_wrapper`. So I think it's close to correct, but there still seems to be an issue where some aren't being merged.

Btw, you can test this locally. How I do it is:
```
F:\source\llvm-project>llvm\out\build\x64-Debug\bin\clang-tblgen.exe -o clang\docs\AttributeReference.rst -gen-attr-docs clang\include\clang\Basic\Attr.td -I clang\include\

F:\source\llvm-project\clang\docs>cd clang\docs

F:\source\llvm-project\clang\docs>make html
```
Then I open at the output in `file:///F:/source/llvm-project/clang/docs/_build/html/AttributeReference.html` in my web browser and look around at the generated HTML. (This does require your python to have sphinx installed, which you can get through `pip`.)

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