FACE_X:null = 0
PlaneMesh will face the positive X-axis.
FACE_Y:null = 1
PlaneMesh will face the positive Y-axis. This matches the behavior of the
PlaneMesh in Godot 3.x.
FACE_Z:null = 2
PlaneMesh will face the positive Z-axis. This matches the behavior of the QuadMesh in Godot 3.x.