Calculate coordinate mapping after drawing figure

[has2k1]

To calculate accurate coordinate mappings for matplotlib (& plotnine) plots
in display coordinates, the figure should know the location of it's subplots.

The location determined by the subplot parameters (subplot_params) and they
come from one or more of these sources, listed from lowest to highest priority:

1. rcParams
2. plt.subplots(..., gridspec_kw={..., **subplot_params})
3. fig.subplot_adjust(**subplot_params)
4. layout engine

The layout engine has the last say as it dynamically calculates subplot_params
and calls fig.subplot_adjust() to set them.

There are two things to consider:

1. Only layout engines that are "adjust_compatible" calculate subplot_params
2. Matplotlib runs the layout engine only when drawing the figure

This PR ensures that there is an "adjust_compatible" layout engine and the plot
is drawn/saved before the coordinate mappings are calculated.

closes has2k1/plotnine#738

[wch]

UPDATE: Disregard this comment below -- it looks like I had problems checking out the branch, and so I was still using main for testing this.

I think I still have problems when using this change.

In the screenshot below, notice that for the brush, the xmin/xmax/ymin/ymax are noticeably different from the actual bounds of the rectangle. This is more noticeable if you use a wide window.

This is using the code from https://shinylive.io/py/examples/#basic-plot-interaction (but running locally with regular shiny, not shinylive)

[wch]

Thank you!