Compute any additional function evaluations needed for the dense output
of the last accepted step, and store them in me%funcs (after the ones used by
the step function). This is the default for methods that don't need any.
This is called by interpolate (once per step, and only if the dense output
is used). The step is defined by me%dense_t, me%dense_h, me%dense_x, and me%dense_xf.
Nodes of different colours represent the following:
Solid arrows point from a procedure to one which it calls. Dashed
arrows point from an interface to procedures which implement that interface.
This could include the module procedures in a generic interface or the
implementation in a submodule of an interface in a parent module.