[clang] [LifetimeSafety] Refactor FactGenerator to use RecursiveASTVisitor (PR #153661)

[Gábor Horváth via cfe-commits]

Xazax-hun wrote:

Thanks! 

I have one more question. So we need the reverse post order property of the CFG to ensure that we visit everything in the right order. The only reason why I am a bit unsure here, is because I wonder if it can ever cause some trouble that the RAV visiting the subexpressions is crossing a basic block boundary and venturing into that block too early, before all of its predecessors have been visited. 

If this cannot happen, I think the current approach should be fine. 

https://github.com/llvm/llvm-project/pull/153661