[clang] [clang][analyzer] Change modeling of 'fileno' in checkers. (PR #81842)

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https://github.com/NagyDonat approved this pull request.

LGTM with some low priority bikeshedding in a comment.

By the way it would be good to rebase this change onto your other commit #79312 (that was merged a few hours ago) and use the "toolbox" introduced there if that's possible.

https://github.com/llvm/llvm-project/pull/81842