Reapply "[analyzer] Accept C library functions from the `std` namespace" again (#85791)

This reapplies 80ab8234 again, after
fixing a name collision warning in the unit tests (see the revert commit
13ccaf9b

 for details).

In addition to the previously applied changes, this commit also clarifies the
code in MallocChecker that distinguishes POSIX "getline()" and C++ standard
library "std::getline()" (which are two completely different functions). Note
that "std::getline()" was (accidentally) handled correctly even without this
clarification; but it's better to explicitly handle and test this corner case.

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Co-authored-by: Balazs Benics <benicsbalazs@gmail.com>