Curves: Move curves primitive to object add code

Currently, any time a Curves data-block is created, the `curves_random`
function runs, filling it with 500 random curves, also adding a radius
attribute. This is just left over from the prototype in the initial
commit that added the type.

This commit moves the code that creates the random data to the curve
editors module, like the other primitives are organized.

Differential Revision: https://developer.blender.org/D14211

source/blender/editors/include/ED_curves.h

@@ -15,3 +15,14 @@ void ED_operatortypes_curves(void);
 #ifdef __cplusplus
 }
 #endif
+
+#ifdef __cplusplus
+
+#  include "BKE_curves.hh"
+
+namespace blender::ed::curves {
+
+bke::CurvesGeometry primitive_random_sphere(int curves_size, int points_per_curve);
+
+}
+#endif