[clang] [clang][analyzer] fix crash when modelling 'getline' function in checkers (PR #145229)

[Baranov Victor via cfe-commits]

vbvictor wrote:

> Your concern that "However, we will still try to model "incorrect" getline methods, wasting cpu." is very premature optimization, the runtime change would be totally negligible

Indeed, without measurements, this argument is not viable.

I've investigated the code of `StdLibraryFunctionsChecker` and the part that deals with function signatures can be extracted in separate file without many problems.

For now, I can implement more error-handling as in option 2 and refactor `StdLibraryFunctionsChecker` later if needed.

https://github.com/llvm/llvm-project/pull/145229