Allow parse-time evaluation of calls, pipelines and subexpressions (#9499)

Co-authored-by: Antoine Stevan <44101798+amtoine@users.noreply.github.com>

crates/nu-command/tests/commands/path/split.rs

@@ -25,3 +25,13 @@ fn splits_correctly_single_path() {
 
     assert_eq!(actual.out, "spam.txt");
 }
+
+#[test]
+fn splits_correctly_single_path_const() {
+    let actual = nu!(r#"
+        const result = ('home/viking/spam.txt' | path split);
+        $result | last
+    "#);
+
+    assert_eq!(actual.out, "spam.txt");
+}