refactor backend type lists

Hello

We have lists of backend types scattered through the tree.  I found two
current ones, and Euler Taveira wants to add a couple more[1].  His
patch is actually blocked on not adding more, so this seems worth doing.
Bikeshedding welcome (for a limited time).

[1] https://postgr.es/m/313aa202-b5fa-4e3f-95d0-83425575c66d@app.fastmail.com

A couple points.  First, launch_backend.c has its own strings for
process names, inconsistent with the ones in miscinit.c.  I think we
should ignore the ones in launch_backend.c, because they're less
polished and not used for anything interesting, whereas the ones in
miscinit.c::GetBackendTypeDesc() are -- particularly init_ps_display and
pg_stat_activity.

Second, in discussion [2] leading to commit 18d67a8d7d30 (Nov 2024) it
was agreed to add support for translating backend type descriptions.
I'm not really sure that this is useful.  It would be, if set_ps_display
and pg_stat_activity used translated names, so that you could match what
log messages say with what the process lists show.  But I think we've
historically not translated those.  We have a few translatable strings
as the argument of HandleChildCrash() in postmaster.c, but those are
using names that are yet a third source of strings; I'm not a fan of
this.  (For staters, if a translation decided to use non-ascii chars for
process names, would that work okay in set_ps_display?  I bet it
wouldn't, because that's using strlen()).  So I would propose to rewind
a bit here, and remove translation from all those places so that the
output is consistent (== usable) between log messages and ps/pg_stat_activity.

[2] https://www.postgresql.org/message-id/flat/a102f15f-eac4-4ff2-af02-f9ff209ec66f%40iki.fi


Third, I didn't do it here, but HandleChildCrash is currently called
like
                HandleChildCrash(pid, exitstatus,
                                 _("WAL writer process"));
creating yet another source of strings to describe process types.

I think it would be much better to avoid that by using
                HandleChildCrash(pid, exitstatus,
                                 _(GetBackendTypeDesc(B_WAL_WRITER));

instead.  If we decide to get rid of the translation, then
                HandleChildCrash(pid, exitstatus,
                                 GetBackendTypeDesc(B_WAL_WRITER);

This last one would be my preference actually.  Note that we use this
string in an error that looks like this (LogChildExit):

        /*------
          translator: %s is a noun phrase describing a child process, such as
          "server process" */
                (errmsg("%s (PID %d) exited with exit code %d",
                        procname, pid, WEXITSTATUS(exitstatus)),

I would change this to
errmsg("process %d of type \"%s\" exited with exit code %d",
       pid, procname, WEXITSTATUS())
Note that in the original, the process name is translated, and in my
proposal it wouldn't be.  (This helps match the log message with "ps"
and pg_stat_activity).


Fourth: patch 0002 is a necessary hack to get the proctype_list.h
strings be picked up for translation by gettext in makefiles.  It's
quite ugly!  I'd rather not have it at all.  I have no idea how to do
this in Meson.

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
"I dream about dreams about dreams", sang the nightingale
under the pale moon (Sandman)