FAMILY-dependent apostrophe behaviour with -mom

[Marc Simpson]

Hi all,

I've noticed a difference in the typesetting of apostrophes depending
on selected font family with groff -mom.

Steps to reproduce (GNU groff version 1.22.4, from MacPorts):

- Fetch Peter Schaffter's font installation script from
  https://www.schaffter.ca/mom/bin/install-font.sh.
  - (Peter, if you're here: thanks for 'mom' and this script!)
- Install a macOS system font, e.g. Georgia; I did this interactively,
  creating Georgia +R, +I, +B and +BI.
- Typeset the following (minimal) document:

  --8<------------------------
  .PRINTSTYLE TYPESET
  \#.FAMILY H
  \#.FAMILY Georgia
  .START
  .PP
  Here's an example.
  --8<------------------------

- Note how the apostrophe is typeset as ’ (closing single quotation
  mark) with Times.
- Specify another builtin FAMILY, like H (uncomment line 2); typeset
  and observe the same.
- Now specify that the document is should be typeset in Georgia
  instead (comment out line 2, uncomment line 3).
- Note that the apostrophe is now typeset as ' (a typewriter quote).

Workaround: specify

  .char ' \[cq]

before START.  Note too that this is what .CODE OFF is doing; my
document originally had _inconsistent_ straight and curly apostrophes
as a result of interleaved code blocks.

It's unclear to me why this behaviour differs on the basis of family;
is this a bug, a difference caused by installing a custom font, or
simply user error?  (If the behaviour is intentional, then there's a
related state bug in CODE toggling.)

Thanks,
Marc