[Analyzer][NFC] Iterator Checkers - Separate iterator modeling and the actual checkers

A monolithic checker class is hard to maintain. This patch splits it up
into a modeling part, the three checkers and a debug checker. The common
functions are moved into a library.

Differential Revision: https://reviews.llvm.org/D70320

GitOrigin-RevId: afb13afcf2232c81fe8097832e5b6a2bde6bb3a5
9 files changed