Awkward plotting of trajectory and dataset

[zouter]

After inferring a trajectory, the expression and original dimred are no longer present in the trajectory object. This is fine, but requires that you add all the relevant information to the trajectory object first before plotting.

trajectory <- trajectory %>% 
  add_expression(counts = dataset$counts, expression = dataset$expression, expression_projected = dataset$expression_projected) %>% 
  add_dimred(dyndimred::dimred_landmark_mds)

dynplot(trajectory) +
  geom_cell_point(aes(color = select_expression(mapper("Dpp4")))) +
  geom_velocity_arrow(color = "black", size = 2) +
  geom_velocity_arrow(color = "white") +
  geom_trajectory_segments(color = "white", size = 2, shadow = shadow_defaults(size = 2))

How can we improve this?