[clang] [analyzer][docs] Further improve the optin.core.FixedAddressDereference docs (PR #182037)

[Balázs Benics via cfe-commits]

steakhal wrote:

<img width="1190" height="762" alt="Screenshot 2026-02-18 at 14 55 19" src="https://github.com/user-attachments/assets/887bf0fc-9b38-48fd-9025-8daf0cd22f9e" />


https://github.com/llvm/llvm-project/pull/182037