[MTE] Convert StackSafety into analysis

This lets us to remove !stack-safe metadata and
better controll when to perform StackSafety
analysis.

Reviewers: eugenis

Subscribers: hiraditya, steven_wu, dexonsmith, cfe-commits, llvm-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D80771