[WIP] Get ARCore working for 4.x

[paddy-exe]

I tried to orient myself around the guides from David's PR dicussion: https://github.com/godotengine/godot/pull/78859

I haven't tested the changes yet. I would like to receive feedback for a good implementation.

[paddy-exe]

This last commit implements the needed methods for the ARCoreInterface class such as

• get_activity()
• get_surface()
• is_activity_resumed()
• get_display_rotation() -> will be added in ongoing upstream PR: https://github.com/godotengine/godot/pull/77559

Talked about with @m4gr3d on the last GDExtension meeting.

[paddy-exe]

Closing as now no longer needed.