feat(clap_derive): Add default_values_t and default_values_os_t for Vec field types

[emersonford]

Implements #3932

[emersonford]

hm as I coded this up, I realized I could apply this for all Vec<impl Display>, not just a Vec<impl ValueEnum>.

this would be out of scope of #3932, but I'll push another commit with this change as I feel might as well handle it in the same PR? can always reset back to the single commit and submit another PR otherwise :)

[emersonford]

@epage just pushed the changes to address all of your comments (aside from the swapping multi_value ones as those are no longer relevant when using default_values_t)

[epage]

Once the ui tests are passing, I'll merge this.

master is now for clap v4. Once this is merged, if you want you can then cherry-pick this back to v3-master branch and submit a new PR.

[emersonford]

that was a bit annoying, my local cargo test output differs from the Github actions cargo test output, so took a minute to resolve. but looks like the test pass now @epage, will submit a PR to cherry pick back to v3 shortly. :)