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-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();