fix(parser): span of keyword expression (#14928)

# Description

This PR fixes #14816 , so that expression-contains-position check won't
need special treatment for keyword expressions.
e.g.

```nushell
overlay use foo as bar
                  # |_______ cursor here

if true { } else { }
                # |_______ here
```

as mentioned in #14924

# User-Facing Changes

# Tests + Formatting

# After Submitting

crates/nu-parser/src/parser.rs

@@ -919,7 +919,7 @@ pub fn parse_multispan_value(
             Expression::new(
                 working_set,
                 Expr::Keyword(Box::new(keyword.clone())),
-                arg_span,
+                keyword.span.merge(keyword.expr.span),
                 keyword.expr.ty,
             )
         }