Similarly to `Vector2` and `Rect2` transforms in 2D and Vector3, Plane,
and AABB in 3D. PoolVector2Array and PoolVector3Array were the only
missing Variant types in both Transform2D and Transform respectively.
This allows more consistency in the manner we include core headers,
where previously there would be a mix of absolute, relative and
include path-dependent includes.
Aaron Franke
Andrii Doroshenko (Xrayez)
Juan Linietsky
Rémi Verschelde