The actual coordinates that define a polygon are actually local, the position of
Polygon2D doesn't automatically shift all the coordinates defined by the polygon for it to be represented in global coordinates, you can use an overridden
xform method for translating an array of points.
transform_points_2d is removed since 3.2.beta in favor of
xform, see this PR.
var trans = Transform2D(0.0, get_global_mouse_position())
var polyB = trans.xform(adder.get_polygon())
mergeResult = Geometry.merge_polygons_2d(levelVec2, polyB)
levelVec2 polygon needs to be transformed perhaps.
merge_polygons_2d will return an empty array if neither polygon overlap.