The alignment of the marker, which controls where the child is drawn
and how the anchor of the marker widget and screen position are interpreted.
Defaults to Alignment.center, but with marker like location icon, you might want to use Alignment.bottomCenter.
The bearing of the marker, in degrees clockwise from north.
This value will be normalized to be in the range 0, 360.
You can get bearing/heading from GPS location,
If only use StaticMarker to add a non-moving marker, you can set this value to 0