[clang] [Clang][Docs] Add documentation for the address_space attribute (PR #181924)

[Reid Kleckner via cfe-commits]

https://github.com/rnk commented:

PTAL, I rendered the docs locally, I don't see any rendering bugs:

<img width="1144" height="594" alt="Image" src="https://github.com/user-attachments/assets/284b8339-7629-4805-8162-deb0573b9dab" />

https://github.com/llvm/llvm-project/pull/181924