This updates the multi-command argument parsing code to leverage parent

argparsers. This is a method of defining common sets of arguments that

can be populated once up-front and then used by other argument parsers,

avoiding duplication and in theory helping with option resolution.
We now define a common option parser for the --help, --debug, and

--json global arguments, along with any common subparser options

defined in common_subcommand_option_list. This is shared by all

subcommands.
This isn't really fundamentally different than re-creating the options,

like we were doing before, but it does better define how options are

expected to be shared and reduces the work that must be done at argument

parser creation time.
Originally, the global options were also being shared with the main

argument parser, but this ended up causing problems where --json on

the main command would override that on the subcommand. This could be

solved by unsetting defaults for any global options and marking the

default as "suppress", but this was invasive (requiring other commands

to check for the presence of options.json_output) and probably not

worth doing. So for now, only subcommands share the options.

Tested all rbt review commands and options (along with an upcoming fix)

and the in-progress rbt status-update rewrite. Verified that all options

worked as expected.
Also checked the help output for each main command subcommand, checking

results.