Tailor CLI feedback about "arc alias" to describe shell command aliases

Summary:
Fixes T9873. Instead of printing something like this:

Aliased "arc ls" to "arc !ls".

...print this:

Aliased "arc ls" to shell command "ls".

Test Plan:

• Added shell commands and internal aliases.
• Removed aliases.
• Listed aliases.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9873

Differential Revision: https://secure.phabricator.com/D14651