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

[Reid Kleckner via cfe-commits]

rnk wrote:

I added information about the TR and qualifiers, and I think I'm going to go ahead and push this as an improvement over the status quo before I get more suggestions for improvement. :) Additional PRs are welcome.

<img width="1162" height="679" alt="Screenshot 2026-02-18 at 12 56 24 PM" src="https://github.com/user-attachments/assets/a6659f3d-5941-400b-8e36-063667498b47" />


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