### Godot version

v4.1.1.stable.official [bd6af8e0e]

### System information

Godot v4.1.1.stable - Debian GNU/Linux trixie/sid trixie - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1060 (nvidia) - Intel(R) Core(TM) i5-8400 CPU @ 2.80GHz (6 Threads)

### Issue description

`Area2D`s which extend beyond the bounds of the root viewport, eg. when using a `canvas_items` stretch mode, receive mouse input events even in the black bands letterboxing the game:

https://github.com/godotengine/godot/assets/441188/3beb962f-c1fa-4098-a375-f3d862013577


### Steps to reproduce

1. Set project stretch mode to either `canvas_items` or `viewport`
2. Have an `Area2D` whose `CollisionShape` extends beyond the bounds of the rendered region
3. Connect the `Area2D`'s `mouse_[entered|exited]` signal to something
4. Wave the mouse around in the black areas outside the rendered game

### Minimal reproduction project

Project used for video demo above:

[area2d-oob.zip](https://github.com/godotengine/godot/files/12207031/area2d-oob.zip)

This only demos `mouse_[entered|exited]`, but I first encountered this with the `Area2D.input_event` signal, where it received mouse clicks as well.
GDCLASS(SubViewport, Viewport);
public:
	enum ClearMode {
		CLEAR_MODE_ALWAYS,
		CLEAR_MODE_NEVER,
		CLEAR_MODE_ONCE
	};
	enum UpdateMode {
		UPDATE_DISABLED,
		UPDATE_ONCE, 
		UPDATE_WHEN_VISIBLE, 
		UPDATE_WHEN_PARENT_VISIBLE,
		UPDATE_ALWAYS
	};
private:
	UpdateMode update_mode = UPDATE_WHEN_VISIBLE;
	ClearMode clear_mode = CLEAR_MODE_ALWAYS;
	bool size_2d_override_stretch = false;
	void _internal_set_size(const Size2i &p_size, bool p_force = false);
protected:
	static void _bind_methods();
	virtual DisplayServer::WindowID get_window_id() const override;
	void _notification(int p_what);
public:
	void set_size(const Size2i &p_size);
	Size2i get_size() const;
	void set_size_force(const Size2i &p_size);
	void set_size_2d_override(const Size2i &p_size);
	Size2i get_size_2d_override() const;
	void set_size_2d_override_stretch(bool p_enable);