There's no need to have a method to convert a T-Spline to a B-Rep model because Fusion does this automatically when you leave the "Form" mode. You can see this if you create a new part, create a new T-Spline model, and then write a program to get the BRepBody objects available in the root component. You should see one, which is a result of the T-Spline being converted to a B-Rep.