Improve support for nonstandard data representation in relplot

[mwaskom]

• Suppress internal names for anonymous vector objects from appearing as axis labels (fixes Unnecessary y-label in relplot #2712)
• Support anonymous vector objects as faceting variables (fixes relplot does not handle numpy-types for dimensional variables #2624)

[codecov]

Codecov Report

Merging #2846 (8194887) into master (8bae24f) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2846   +/-   ##
=======================================
  Coverage   98.05%   98.05%           
=======================================
  Files          69       69           
  Lines       22218    22227    +9     
=======================================
+ Hits        21786    21795    +9     
  Misses        432      432           

Impacted Files	Coverage Δ
seaborn/distributions.py	96.27% <100.00%> (ø)
seaborn/relational.py	99.69% <100.00%> (+<0.01%)	⬆️
tests/test_relational.py	99.28% <100.00%> (+<0.01%)	⬆️

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