This PR adds the options `pp.piBinderNames` and
`pp.piBinderNames.hygienic`. Enabling `pp.piBinderNames` causes
non-dependent pi binder names to be pretty printed, rather than be
omitted. When `pp.piBinderNames.hygienic` is false (the default) then
only non-hygienic such biner names are pretty printed. Setting `pp.all`
enables `pp.piBinderNames` if it is not otherwise explicitly set.
Implementation note: this is exposing the secret pretty printer option
`pp.piBinderNames` that was being used within the signature pretty
printer.
Closes#1134.
Many of our tests in `tests/lean/run/` produce output from `#eval` (or
`#check`) statements, that is then ignored.
This PR tries to capture all the useful output using `#guard_msgs`. I've
only done a cursory check that the output is still sane --- there is a
chance that some "unchecked" tests have already accumulated regressions
and this just cements them!
In the other direction, I did identify two rotten tests:
* a minor one in `setStructInstNotation.lean`, where a comment says `Set
Nat`, but `#check` actually prints `?_`. Weird?
* `CompilerProbe.lean` is generating empty output, apparently indicating
that something is broken, but I don't know the signficance of this file.
In any case, I'll ask about these elsewhere.
(This started by noticing that a recent `grind` test file had an
untested `trace_state`, and then got carried away.)
