ggdist: Visualizations of distributions and uncertainty

Breaking changes:

• The positioning of geom_slabinterval() family geoms when using position_dodge() is now slightly different in order to match up with how other geoms are positioned (#85). This may slightly change existing charts that use position = "dodge", and in some cases may cause slabs to be drawn slightly outside plot boundaries, but makes it much easier to combine geom_slabinterval() with other geoms in the expected way. If dodging more similar to the old approach is needed, use the new "justification-preserving dodge", position_dodgejust(), in place of position_dodge().

New features:

• For geom_slabinterval(), side, justification, and scale can now be used as aesthetics instead of parameters, allowing them to vary across slabs within the same geom.
• Varying fills within a slab in geom_slabinterval() can now be drawn as true gradients rather than segmented polygons in R >= 4.1 by setting fill_type = "gradient". This substantially improves the appearance of gradient fills in graphics engines that support it (#44).
• Improved support for discrete distributions:
  • stat_dist_slabinterval() and company now detect discrete distributions and display them as histograms (#19).
  • geom_dotsinterval() now adjusts bin widths on discrete distributions when they would result in bins that are taller than the allocated space to ensure that they fit within the required space (#42).
• Allow user-specified lower and/or upper bounds on dynamic geom_dotsinterval() bin width by passing a vector of two values to the binwidth parameter.
• The automatic bin selection algorithm used by geom_dotsinterval() has been factored out and exported as find_dotplot_binwidth() and bin_dots() for others to use (#77).
• Previously, curve_interval() used a common (but naive) approach to finding a cutoff on data depth to identify the X% "deepest" curves, simply taking the envelope around the X% quantile of curves ranked by depth. This is quite conservative and tends to create intervals that are too wide; curve_interval() now searches for a cutoff in data depth such that X% of curves are contained within its envelope (#67).
• point_interval() and company now accept distributional objects and posterior::rvar()s (full support for distributional objects requires distributional > 0.2.2).
• Reduce dependencies substantially, making the geoms more suitable for use by other packages (thanks to Brenton Wiernik for the help).

New documentation:

• Substantial improvements to the documentation of aesthetics and computed variables in geom_slabinterval(), stat_slabinterval(), and company, listing all custom aesthetics, computed variables, and their usage.

• Several new examples in vignette("slabinterval"), including "rain cloud" plots and an example of histograms for discrete analytical distributions.

Bug fixes:

• Ensure stat_dist_slabinterval() preserves group order (#88).
• Improve test coverage up to ~96%.
• Restore computed variable n for stat_sample_slabinterval().
• Various improvements in correct NA handling across the geoms (#74, #51).