[analyzer][StreamChecker] Using function description objects - NFC.

Summary:
Have a description object for the stream functions
that can store different aspects of a single stream operation.

I plan to extend the structure with other members,
for example pre-callback and index of the stream argument.

Reviewers: Szelethus, baloghadamsoftware, NoQ, martong, Charusso, xazax.hun

Reviewed By: Szelethus

Subscribers: rnkovacs, xazax.hun, baloghadamsoftware, szepet, a.sidorin, mikhail.ramalho, Szelethus, donat.nagy, dkrupp, gamesh411, Charusso, martong, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D75158