Try to make hide-env respects overlays (#15904)

# Description
Closes: #15755
I think it's a good feature, to achieve this, we need to get all hidden
envs(it's defined in `get_hidden_env_vars`, and then restore these envs
back to stack)

# User-Facing Changes
### Before
```nushell
> $env.foo = 'bar'
> overlay new xxx
> hide-env foo
> overlay hide xxx
> $env.foo
Error: nu:🐚:column_not_found

  × Cannot find column 'foo'
   ╭─[entry #21:5:1]
 4 │ overlay hide xxx
 5 │ $env.foo
   · ────┬───┬
   ·     │   ╰── value originates here
   ·     ╰── cannot find column 'foo'
   ╰────
```

### After
```nushell
> $env.foo = 'bar'
> overlay new xxx
> hide-env foo
> overlay hide xxx
> $env.foo
bar
```

## Note
But it doesn't work if it runs the example code in script:
`nu -c "$env.foo = 'bar'; overlay new xxx; hide-env foo; overlay hide
xxx; $env.foo"`
still raises an error says `foo` doesn't found. That's because if we run
the script at once, the envs in stack doesn't have a chance to merge
back into `engine_state`, which is only called in `repl`.

It introduces some sort of inconsistency, but I think users use overlays
mostly in repl, so it's good to have such feature first.

# Tests + Formatting
Added 2 tests

# After Submitting
NaN

crates/nu-cmd-lang/src/core_commands/overlay/hide.rs

@@ -86,12 +86,16 @@ impl Command for OverlayHide {
             vec![]
         };
 
+        // also restore env vars which has been hidden
+        let env_vars_to_restore = stack.get_hidden_env_vars(&overlay_name.item, engine_state);
         stack.remove_overlay(&overlay_name.item);
+        for (name, val) in env_vars_to_restore {
+            stack.add_env_var(name, val);
+        }
 
         for (name, val) in env_vars_to_keep {
             stack.add_env_var(name, val);
         }
-
         Ok(PipelineData::empty())
     }
 

crates/nu-protocol/src/engine/stack.rs

@@ -414,6 +414,37 @@ impl Stack {
         result
     }
 
+    /// Get hidden envs, but without envs defined previously in `excluded_overlay_name`.
+    pub fn get_hidden_env_vars(
+        &self,
+        excluded_overlay_name: &str,
+        engine_state: &EngineState,
+    ) -> HashMap<String, Value> {
+        let mut result = HashMap::new();
+
+        for overlay_name in self.active_overlays.iter().rev() {
+            if overlay_name == excluded_overlay_name {
+                continue;
+            }
+            if let Some(env_names) = self.env_hidden.get(overlay_name) {
+                for n in env_names {
+                    if result.contains_key(n) {
+                        continue;
+                    }
+                    // get env value.
+                    if let Some(Some(v)) = engine_state
+                        .env_vars
+                        .get(overlay_name)
+                        .map(|env_vars| env_vars.get(n))
+                    {
+                        result.insert(n.to_string(), v.clone());
+                    }
+                }
+            }
+        }
+        result
+    }
+
     /// Same as get_env_vars, but returns only the names as a HashSet
     pub fn get_env_var_names(&self, engine_state: &EngineState) -> HashSet<String> {
         let mut result = HashSet::new();

tests/overlays/mod.rs

@@ -856,6 +856,36 @@ fn overlay_hide_renamed_overlay() {
     assert!(actual_repl.err.contains("external_command"));
 }
 
+#[test]
+fn overlay_hide_restore_hidden_env() {
+    let inp = &[
+        "$env.foo = 'bar'",
+        "overlay new aa",
+        "hide-env foo",
+        "overlay hide aa",
+        "$env.foo",
+    ];
+
+    let actual_repl = nu!(nu_repl_code(inp));
+
+    assert_eq!(actual_repl.out, "bar");
+}
+
+#[test]
+fn overlay_hide_dont_restore_hidden_env_which_is_introduce_currently() {
+    let inp = &[
+        "overlay new aa",
+        "$env.foo = 'bar'",
+        "hide-env foo", // hide the env in overlay `aa`
+        "overlay hide aa",
+        "'foo' in $env",
+    ];
+
+    let actual_repl = nu!(nu_repl_code(inp));
+
+    assert_eq!(actual_repl.out, "false");
+}
+
 #[test]
 fn overlay_hide_and_add_renamed_overlay() {
     let inp = &[