When handling tangent 1 or tangent 2 with the handle, update the other tangent based on the split flags.
When merging or splitting the radius or the angle, update the other tangent.
Fix BLinePointTangentMerge and BLinePointTangentSplit to properly use the new members of BLinePoint
Add actions to split/merge angle/radius of tangents individually.
Use the new members of BLinePoint correctly in the layers.
Do not assume that parent of BLinePoint is always a LinkableValue Node
Allow widget curves to draw all the components of the BlinePoint