`App::get_matches` lazily post-processes `App`s and `Arg`s so we don't
do it to subcommands that are never run (downside being people have to
exercise their full app to get debug_asserts).
`clap_generate` was only post-processing the top-level `App` and `Arg`s,
ignoring the sub-commands. In #2858, we noticed that `--version` was
being left in the completions instead of being removed during the
`_build` step. We would also have an incorrect `num_vals` and a host of
other problems.
This change adds a `App::_build_all` function for `clap_generate` to use
to eagerly build everything. By having it there, we make sure
everywhere that needs eager building, gets it (like some tests).
In `clap_generate::utils`, we add a unit test to ensure the subcommand's
`--version` was removed.
For some other tests specifying `.version()`, I added
`AppSettings::PropagateVersion` to make it behave more consistently.
The places I didn't were generally where the version was conditionally
set.
For `clap_generate/tests/generate_completions.rs`, I had to adjust the
`conflicts_with` because the subcommand was inheriting the argument with
it defined *but* the subcommand did not have the argument, tripping up a
debug assert.
Fixes#2860
