This PR makes `#guard_msgs` to treat `trace` messages separate from
`info`, `warning` and `error`. It also introduce the ability to say
`#guard_msgs (pass info`, like `(drop info)` so far, and also adds
`(check info)` as the explicit form of `(info)`, for completeness.
Fixes#8266
This PR fixes a bug that could cause the `injectivity` tactic to fail in
reducible mode, which could cause unfolding lemma generation to fail
(used by tactics such as `unfold`). In particular,
`Lean.Meta.isConstructorApp'?` was not aware that `n + 1` is equivalent
to `Nat.succ n`.
Closes#5064
