[analyzer][NFC] Use CallEvent checker callback in GenericTaintChecker

Summary:
Intended to be a non-functional change but it turned out CallEvent handles
constructor calls unlike CallExpr which doesn't triggered for constructors.

All in all, this change shouldn't be observable since constructors are not
yet propagating taintness like functions.
In the future constructors should propagate taintness as well.

This change includes:
 - NFCi change all uses of the CallExpr to CallEvent
 - NFC rename some functions, mark static them etc.
 - NFC omit explicit TaintPropagationRule type in switches
 - NFC apply some clang-tidy fixits

Reviewers: NoQ, Szelethus, boga95

Reviewed By: Szelethus

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

Tags: #clang

Differential Revision: https://reviews.llvm.org/D72035

Author: steakhal