ScrollContainer doesn't respect _clips_input override

[rgson]

Godot version:
3.2.2.stable.official

OS/device including version:
Debian 10

Issue description:
ScrollContainer clips input by default and ignores implementations of _clips_input.

Steps to reproduce:

1. Create a ScrollContainer
2. Disable "Rect > Clip Content" and make it smaller than the full screen (to actually see the clipped content)
3. Fill it with enough buttons for a scroll bar to appear
4. Attach a script to it to disable input clipping:

extends ScrollContainer

func _clips_input():
	return false

5. Try clicking the buttons that are outside of the ScrollContainer's bounds. They're still not clickable.

Minimal reproduction project:
scrollcontainer_clips_input.zip

---

It's straight-forward to see that this is caused by an override of clips_input in scroll_container.cpp that always returns true without consulting the attached script. The original implementation in control.cpp does delegate to the attached script as documented.

My suggestion would be to add the same delegation to the implementation in scroll_container.cpp.

 bool ScrollContainer::clips_input() const {
+	if (get_script_instance()) {
+		return get_script_instance()->call(SceneStringNames::get_singleton()->_clips_input);
+	}
 	return true;
 }