don't include import path in args to aliased external commands (#14231)

Fixes #13776

# User-Facing Changes

Arguments to aliased externals no longer include nested import paths:

```diff
module foo { export alias bar = ^echo }
use foo
foo bar baz
-bar baz
+baz
```

crates/nu-parser/src/parser.rs

@@ -1343,10 +1343,10 @@ pub fn parse_call(working_set: &mut StateWorkingSet, spans: &[Span], head: Span)
                 trace!("parsing: alias of external call");
 
                 let mut head = head.clone();
-                head.span = spans[0]; // replacing the spans preserves syntax highlighting
+                head.span = Span::concat(&spans[cmd_start..pos]); // replacing the spans preserves syntax highlighting
 
                 let mut final_args = args.clone().into_vec();
-                for arg_span in &spans[1..] {
+                for arg_span in &spans[pos..] {
                     let arg = parse_external_arg(working_set, *arg_span);
                     final_args.push(arg);
                 }