Research adding and design API for polar coordinate systems

https://nbviewer.org/github/JetBrains/lets-plot-kotlin/blob/master/docs/examples/jupyter-notebooks/f-4.7.0/coord_polar.ipynb

Start by reviewing docs/examples/jupyter-notebooks/f-4.7.0/coord_polar.ipynb through the linked nbviewer example to understand the polar-coordinate requirements. Research and document a suitable API design for adding polar coordinate systems to Kandy; done means the design and implementation scope are clear.

Written by the indexing model from the issue text.