Use a stable algorithm in sorting marks

[mwaskom]

Closes #3059. With the example from that issue:

(
    so.Plot(x=falseposrate_logistic, y=trueposrate_logistic)
    .add(so.Line(marker="o", pointsize=2))
)

I wasn't able to cook up a toy example to demonstrate the problem so I haven't added a separate test for it. Would be a great addition if anyone can come up with one (i.e. not involving scikit learn, etc.).

[codecov]

Codecov Report

Merging #3064 (8f9c372) into master (c412ddf) will not change coverage.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3064   +/-   ##
=======================================
  Coverage   98.38%   98.38%           
=======================================
  Files          72       72           
  Lines       23537    23537           
=======================================
  Hits        23156    23156           
  Misses        381      381           

Impacted Files	Coverage Δ
seaborn/_marks/area.py	96.51% <100.00%> (ø)
seaborn/_marks/line.py	100.00% <100.00%> (ø)