This makes loading almost all commands faster, since only one module
file is loaded rather than all of them. There is one main exception,
dealing with 'help'. Running `./mach help` (or -h or --help) requires
the description text for every command, so every module file is still
loaded.
We could expand this improvement here to consolidate all commands and
their parameters in this `MACH_COMMANDS` dict, but the only two benefits
are improving help, and not having two places where the commands are
specified (their file, and this dict).
There's a lot of extra work needed to do that, especially for handling
sub commands, and it did not seem worth the cost for the benefit at this
time.
Depends on D180499
Differential Revision: https://phabricator.services.mozilla.com/D180500
9d4f0e9997