Core: Some code style improvements to AStarGrid2D

[dalexeev]

1. Remove unused, undefined and unexposed get_width() and get_height() declarations.
2. Replace GET_POINT_UNCHECKED() macro with _get_point_unchecked() method, for consistency and better style.
3. Replace int64_t with int32_t since components of Vector2i and Rect2i are int32_t.
4. Make loops consistent.

[Chaosus]

I think these int's should also been changed to int32_t for consistency, other than that I have no claim to this PR.

[dalexeev]

I think these int's should also been changed to int32_t for consistency

Done. Although this is not related to coordinates and Vector/Array use int.

godot/core/templates/vector.h

Line 96 in 571cd0e

_FORCE_INLINE_ const T &operator[](int p_index) const { return _cowdata.get(p_index); }

[akien-mga]

Thanks!