FIX: use compound paths to draw transformed geometries

[rcomer]

Rationale

When a geometry gets transformed to a different crs, it can become multiple geometries. Currently we plot these as separate paths which could be problematic if the user passes a list of e.g. facecolors.

import matplotlib.pyplot as plt
import cartopy.crs as ccrs
import shapely.geometry as sgeom

square1 = sgeom.Polygon([(-10, -10), (10, -10), (10, 10), (-10, 10), (-10, 10) ])
square2 = sgeom.Polygon([(30, 0), (50, 0), (50, 20), (30, 20), (30, 0)])

fig = plt.figure(figsize=(4, 5))

ax1 = fig.add_subplot(211, projection=ccrs.PlateCarree())
ax2 = fig.add_subplot(212, projection=ccrs.PlateCarree(central_longitude=180))

for ax in ax1, ax2:
    ax.coastlines()
    ax.add_geometries([square1, square2], crs=ccrs.PlateCarree(),
                      facecolors=['r', 'b'])

plt.show()

Before:

After:

Implications

[rcomer]

Diff looks like