This PR adds infrastructure to help diagnose cases where tactics like
`unfold`
leave the goal in a state that is type-correct only at `.default`
transparency,
causing `rw`/`simp` to fail at `.instances` transparency.
Changes:
- Add a `transparency` parameter to `Meta.check` (defaults to `.all`)
- Add `withInstancesTypeCheckNote` which appends a
lazy note to tactic errors when the target is not type-correct at
`.instances`
- Wrap `rw`, `simp`, `dsimp`, and `simp_all` at the Elab level
- Add opt-in `linter.tacticCheckInstances` that proactively checks every
tactic goal and reports semireducible defs that should be marked
`@[implicit_reducible]`, using diagnostic counter diffing between
`.default`
and `.instances` checks
