Autocomplete: treat aliases as commands in their own right

[autonordev]

Currently, auto-complete will ignore aliases unless there is a direct match. This is problematic because aliases can be helpful in trying to make potentially verbose or unclear command names more memorable, and so excluding them from auto-complete is harmful to the user experience.

This is a change in behaviour, so we should be mindful about developer and user needs, but there would not be any API impact.