eature for all samples in `X`.
feature_values : ndarray of shape (n_grid_points,)
    The feature values for which the predictions have been computed.
ax : Matplotlib axes
    The axis on which to plot the average PD.
pd_line_idx : int
    The sequential index of the plot. It will be unraveled to find the
    matching 2D position in the grid layout.
line_kw : dict
    Dict with keywords passed when plotting the PD plot.
categorical : bool
    Whether feature is categorical.
bar_kw: dict
    Dict with keywords passed when plotting the PD bars (categorical).
r