For example, when running the following:
crates/nu-cli/src
nushell currently parses this as an external command. Before running the command, we check to see if
it's a directory. If it is, we "auto cd" into that directory, otherwise we go through normal
external processing.
If we put a trailing slash on it though, shells typically interpret that as "user is explicitly
referencing directory". So
crates/nu-cli/src/
should not be interpreted as "run an external command". We intercept a trailing slash in the head
position of a command in a pipeline as such, and inject a `cd` internal command.
6f2ef05195