Add get_x and get_y vectorized functions (Point-only)

[jorisvandenbossche]

Awaiting a more complex function to get coordinates in general, adding a simple get_lng/get_lat functions just for points (so those can easily be vectorized)

[jorisvandenbossche]

I see that R's s2 (based on bigquery?) still calls this st_x and st_y, so should we also use get_x and get_y here?

[martinfleis]

should we also use get_x and get_y here?

+1 on that as that is also consistent with shapely.