WIP:Accept Stat and/or Move(s) as anonymous positional args in Plot.add

[mwaskom]

[codecov[bot]]

Codecov Report

Merging #2948 (a63afa8) into master (ae9080d) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2948   +/-   ##
=======================================
  Coverage   98.30%   98.31%           
=======================================
  Files          69       69           
  Lines       23004    23070   +66     
=======================================
+ Hits        22615    22681   +66     
  Misses        389      389           

Impacted Files	Coverage Δ
seaborn/_core/moves.py	100.00% <100.00%> (ø)
seaborn/_core/plot.py	97.37% <100.00%> (+0.03%)	:arrow_up:
tests/_core/test_moves.py	100.00% <100.00%> (ø)
tests/_core/test_plot.py	98.59% <100.00%> (+0.03%)	:arrow_up:
tests/test_axisgrid.py	99.38% <0.00%> (+0.01%)	:arrow_up:
seaborn/axisgrid.py	97.20% <0.00%> (+0.01%)	:arrow_up: