Update core documentation to match recent C# changes

Also a few minor API changes like adding AABB.abs()

Co-authored-by: Rémi Verschelde <rverschelde@gmail.com>

core/math/plane.h

@@ -47,7 +47,6 @@ public:
 	/* Plane-Point operations */
 
 	_FORCE_INLINE_ Vector3 center() const { return normal * d; }
-	Vector3 get_any_point() const;
 	Vector3 get_any_perpendicular_normal() const;
 
 	_FORCE_INLINE_ bool is_point_over(const Vector3 &p_point) const; ///< Point is over plane