This PR updates `rw?`, `show_term`, and other tactic-suggesting tactics
to suggest `expose_names` when necessary and validate tactics prior to
suggesting them, as `exact?` already did, and it also ensures all such
tactics produce hover info in the messages showing tactic suggestions.
This introduces a breaking change in the `TryThis` API: the `type?`
parameter of `addRewriteSuggestion` is now an `LOption`, not an
`Option`, to obviate the need for a hack we previously used to indicate
that a rewrite closed the goal.
Closes#7350
This PR prevents `exact?` and `apply?` from suggesting tactics that
correspond to correct proofs but do not elaborate, and it allows these
tactics to suggest `expose_names` when needed.
These tactics now indicate that a non-compiling term was generated but
do not suggest that that term be inserted. `exact?` also no longer
suggests that the user try `apply?` if no partial suggestions were
found.
This addresses part of #5407 but does not achieve the exact expected
behavior therein (due to #6122).
