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())
     }