[analyzer] Add InvalidPtrChecker

This patch introduces a new checker: `alpha.security.cert.env.InvalidPtr`

Checker finds usage of invalidated pointers related to environment.

Based on the following SEI CERT Rules:
ENV34-C: https://wiki.sei.cmu.edu/confluence/x/8tYxBQ
ENV31-C: https://wiki.sei.cmu.edu/confluence/x/5NUxBQ

Reviewed By: martong

Differential Revision: https://reviews.llvm.org/D97699