Add Spline Curve to Trajectory

Describe the feature

We suggest to extend the Shape tag in OpenSCENARIO, which can up to now only include Polyline (quite simple and trivial trajectories), Clothoid (needs a rework like discussed in https://code.asam.net/simulation/openscenario-1/openscenario/-/issues/506) and NURBS (quite complicated and only start and end point are one the actual trajetory) with a spline curve.

Describe the solution you would like

A spline curve that allows:

• simple manual XML creation
• simple creation from measured data
• simple tool assisted creation
• mathematical simplicity
• appropriate effort for creation vs. effort for evaluation
• C2-continuity
• (to be usable for the OpenDRIVE geometry tag (https://code.asam.net/simulation/opendrive-group/opendrive-standard/-/issues/178) )

Describe alternatives you have considered

Polylines are often to simple and NURBS to complicated. Clothoids need a rework.

Describe the backwards compatibility

Adding a new XOR option to Shape is backward compatible.

Additional context

See related OpenDRIVE issue: https://code.asam.net/simulation/opendrive-group/opendrive-standard/-/issues/178