GH1654 Plotting changes in 3.0

[loicdiridollou]

Adding tests for index.get_loc, changes were already compliant but needed the tests to confirm.
Addressing all changes for the plotting group.

• Index.get_loc() now accepts also subclasses of tuple as keys (BUG: NamedTuples do no match tuples in pandas.Index pandas#57922)
• Series.plot() now correctly handle the ylabel parameter for pie charts, allowing for explicit control over the y-axis label (BUG: Series.plot(kind="pie") does not respect ylabel argument pandas#58239)
• Added missing parameter weights in DataFrame.plot.kde() for the estimation of the PDF (ENH: Allow to plot weighted KDEs. pandas#59337)
• DataFrame.plot.scatter() argument c now accepts a column of strings, where rows with the same string are colored identically (Scatter plot with colour_by and size_by variables pandas#16827 and Meaning of color argument in DataFrame.plot.scatter() pandas#16485)

[cmp0xff]

Thank you @loicdiridollou 🙂