[clang] [WIP][analyzer] Refactor `ExplodedGraph::trim()` (PR #139939)

[Donát Nagy via cfe-commits]

NagyDonat wrote:

This is the cleanup of `ExplodedGraph::trim()` that I promised at https://github.com/llvm/llvm-project/commit/31e981ca1dc323c8a32012cb60a0a8fe3985db1a. This significantly simplifies the algorithm and should be equivalent in a theoretical sense, but unfortunately it changes the (annoyingly fragile) ordering of reports within a bug report equivalence class :disappointed:

@steakhal What should  I do with this?

https://github.com/llvm/llvm-project/pull/139939