[clang][analyzer] Add and change NoteTags in StdLibraryFunctionsChecker.

Change 1: ErrnoChecker notes show only messages related to errno,
not to assumption of success or failure of functions.
Change 2: StdLibraryFunctionsChecker adds its own note about success
or failure of functions, and the errno related note, independently.
Change 3: Every modeled function in StdLibraryFunctionsChecker
should have a note tag message in all "cases". This is not implemented yet,
only for file (stream) related functions.

Reviewed By: donat.nagy

Differential Revision: https://reviews.llvm.org/D153612