make meta part of records visible in mir

[SteveBronder]

Summary

I never knew what the meta part of a record was because when I printed it out in the mir all I got back was <opaque>. Turns out, sometimes they have useful things in them. This PR makes is so that the meta parts of a record are visible in the mir. It makes for a lot more code that's printed out but imo I'd rather have it printed out so I can see what's there.

Release notes

Makes meta records visible in mir instead of <opaque>

Copyright and Licensing

By submitting this pull request, the copyright holder is agreeing to
license the submitted work under the BSD 3-clause license (https://opensource.org/licenses/BSD-3-Clause)

[rybern]

It seems like most of the bloat in the printouts comes from locations, but I'm guessing that's not the parts that's useful for you. Can we keep only the location opaque?

[SteveBronder]

Yeah I'm fine with that. One weird thing, I can just put an opaque_list there but in #885 ocaml 4.12 throws a warning / error for these. Is there some other way to suppress these besides opaque_list? If not then I'm fine doing it anyway and we can sort out how to fix that when we bump up versions

[rybern]

Not sure about that, is opaque_list an alternative to [@sexp.opaque]?

[SteveBronder]

Honestly idk lol I'm gonna just put it on the line number and we can sort it when we update to 4.12

[SteveBronder]

Huh it looks like doing that just puts us back to where we started. Maybe I was just confused since I kept seeing opaque everywhere and we were actually printing the meta in places. Going to close this