Fix cd'ing to symlinked directories (#1651)

* fix: absolutize path against its parent if it was a symlink.

On Linux this happens because Rust calls readlink but doesn't canonicalize the resultant path.

* feat: playground function to create symlinks

* fix: use playground dirs

* feat: test for #1631, shift tests names

crates/nu-test-support/src/playground.rs

@@ -95,6 +95,33 @@ impl Playground {
         self
     }
 
+    pub fn symlink(&mut self, from: impl AsRef<Path>, to: impl AsRef<Path>) -> &mut Self {
+        let from = self.cwd.join(from);
+        let to = self.cwd.join(to);
+
+        let create_symlink = {
+            #[cfg(unix)]
+            {
+                std::os::unix::fs::symlink
+            }
+
+            #[cfg(windows)]
+            {
+                if from.is_file() {
+                    std::os::windows::fs::symlink_file
+                } else if from.is_dir() {
+                    std::os::windows::fs::symlink_dir
+                } else {
+                    panic!("symlink from must be a file or dir")
+                }
+            }
+        };
+
+        create_symlink(from, to).expect("can not create symlink");
+        self.back_to_playground();
+        self
+    }
+
     pub fn with_files(&mut self, files: Vec<Stub>) -> &mut Self {
         let endl = fs::line_ending();