ENH: release the GIL in get_coordinates

[jorisvandenbossche]

Currently the C implementation behind get_coordinates does not release the GIL:

shapely/src/coords.c

Line 459 in 347a3d7

GEOS_INIT;

while it seems we should also be able to use GEOS_INIT_THREADS instead? (I don't think anything inside the core loop depends on the GIL, as at that point the result array is already created, and we just iterate over input geometries)