Allow different names for ...rest (#3954)

* Allow different names for ...rest

* Resolves #3945

* This change requires an explicit name for the rest argument in `WholeStreamCommand`,
  which is why there are so many changed files.

* Remove redundant clone

* Add tests

tests/shell/pipeline/commands/internal.rs

@@ -373,6 +373,25 @@ fn run_custom_command_with_empty_rest() {
     assert_eq!(actual.err, r#""#);
 }
 
+#[test]
+fn run_custom_command_with_rest_other_name() {
+    let actual = nu!(
+        cwd: ".",
+        r#"
+            def say-hello [
+                greeting:string,
+                ...names:string # All of the names
+                ] {
+                    echo $"($greeting), ($names | sort-by | str collect ' ')"
+                }
+            say-hello Salutations E D C A B
+        "#
+    );
+
+    assert_eq!(actual.out, r#"Salutations, A B C D E"#);
+    assert_eq!(actual.err, r#""#);
+}
+
 #[test]
 fn alias_a_load_env() {
     let actual = nu!(