histplot and kdeplot don't follow color cycle with datetime variable

[mwaskom]

This is on purpose, but opening issue to track.

The problem is that drawing the scout with empty data triggers an incorrect auto scale. The current solution is to not follow the color cycle with a datetime variable.

Upstream issue is matplotlib/matplotlib#17586

[mwaskom]

This is fixed upstream, so it would be possible to revert the complexity, but there would be issues with matplotlib <= 3.3

[mwaskom]

Could add a version-specific warning?

[mwaskom]

Actually (filled) plots aren't following the color cycle for any variable type now...

[mwaskom]

Seems to be due to the present of color=None in the function signature, which prevents fill_between (but not plot) from cycling.

This is complicated; I am going to punt for now.