add nearestPoints for prepared geometry

[jaakkor2]

Note: missing tests, I was confused that tests for nearestPoints were duplicated

• https://github.com/JuliaGeo/LibGEOS.jl/blob/v0.8.3/test/test_geos_operations.jl#L144-L154
• https://github.com/JuliaGeo/LibGEOS.jl/blob/v0.8.3/test/test_geos_functions.jl#L431-L448

[visr]

The duplicate tests are a leftover from #149. In that PR src/geos_operations.jl was folded into src/geos_functions.jl. But test/geos_operations.jl still remains. Would be good if you could remove the duplication and put nearestPoints tests in test/geos_functions.jl.

[jaakkor2]

libgeos has nearest points tests in two files

• https://github.com/libgeos/geos/blob/main/tests/unit/capi/GEOSNearestPointsTest.cpp
• https://github.com/libgeos/geos/blob/main/tests/unit/capi/GEOSPreparedNearestPointsTest.cpp

Since the geometries are the same, I though it is a good idea to combine the tests for LibGEOS.jl.