Normalize matplotlib kwargs in scatterplot / lineplot

[mwaskom]

Matplotlib 3.8 makes scatter raise when both long and short forms of arguments are passed (e.g. edgecolor and ec); previously one was silently ignored (I think?).

This is probably a marginal QOL improvement for matplotlib users but has broken the seaborn tests, as scatterplot sets a default edge color using the long-form argument but an example in the docs demonstrates the short-form example

This PR uses keyword argument normalization upstream of where seaborn sets its defaults. The whole situation is kind of a mess and this is just a localized bandaid, but it should get the tests green and marginally improve seaborn usability.