Previously, `cargo help <alias>` resolved the alias and displayed the
help for the targeted subcommand. For example, if `br` were aliased to
`build --release`, `cargo help br` would display the manpage for
cargo-build.

With this patch, it will print "'br' is aliased to 'build --release'".

Co-authored-by: Weihang Lo <weihanglo@users.noreply.github.com>

Co-authored-by: Weihang Lo <weihanglo@users.noreply.github.com>

This changes the behavior so that simple aliases that directly alias a
subcommand (with no arguments) pass-through to that subcommand, while
complex aliases (with arguments) show the alias.

So for example, `cargo help b` will show the manpage for `cargo-build`,
while `cargo help my-alias`, aliased to `build --release`, will show
"`my-alias` is aliased to `build --release`".