Define options and verbs through "magic macros" (#40880)

This is an another alternative for #40656, based on @poettering's
suggestion to use an ELF section.

The output of --help is generated using format-table, but the details of
the formatting a bit off: different sections in the table (verbs, option
groups) are not aligned to the same column. Our current table formatting
doesn't make this easy. If somebody has an idea how to do this without
too much pain, please make suggestions.

Another thing that I didn't know how to do nicely, was to use the two
columns of separation. But maybe this doesn't matter. If we switch to
one column everywhere, I don't think people will care.

Example output:
```console
$ build/systemd-id128 -h | cat
systemd-id128 [OPTIONS...] COMMAND

Generate and print 128-bit identifiers.

Commands:
  new                Generate a new ID
  machine-id         Print the ID of current machine
  boot-id            Print the ID of current boot
  invocation-id      Print the ID of current invocation
  var-partition-uuid Print the UUID for the /var/ partition
  show [NAME|UUID]   Print one or more UUIDs
  help               Show this help

Options:
  -h --help            Show this help
     --version         Show package version
     --no-pager        Do not start a pager
     --no-legend       Do not show headers and footers
     --json=FORMAT     Output inspection data in JSON (takes one of pretty,
                       short, off)
  -j                   Equivalent to --json=pretty (on TTY) or --json=short
                       (otherwise)
  -p --pretty          Generate samples of program code
  -P --value           Only print the value
  -a --app-specific=ID Generate app-specific IDs
  -u --uuid            Output in UUID format

See the systemd-id128(1) man page for details.
```

The output wraps automatically with terminal width. If the terminal is
extremely narrow, ellipsization occurs. I think this doesn't matter
and/or is actually a feature. Such narrow terminals mostly occur in
testing, so it doesn't matter what exactly we do, as long as it is
something somewhat reasonable.

Anyway, I think this is enough as PoC. Please compare this with the
previous approach. /cc @behrmann, @YHNdnzj, @poettering

The three binaries that are converted have options, verbs, optional
arguments, and options terminate option parsing, so most of the
functionality is there. One thing that I didn't implement that was
present in previous PRs is "namespaces", i.e. multiple parsers in the
same source file. I expect that we can handle this similarly to option
groups.

diff --cc src/shared/meson.build
Simple merge