[clang] [clang][analyzer] Support `fgets` in the SteamChecker (PR #73638)

[Balázs Kéri via cfe-commits]

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@@ -778,42 +781,61 @@ void StreamChecker::evalFgetc(const FnDescription *Desc, const CallEvent &Call,
   assertStreamStateOpened(OldSS);
 
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balazske wrote:

Will this invalidate only the buffer, not `F1`?

https://github.com/llvm/llvm-project/pull/73638