optimize capacity & add assert messages in GeoJson

[wjdqhry]

related spring-projects/spring-data-elasticsearch#3063

I found a minor improvement in spring-data-elasticsearch, and I am submitting the same fix here.

I found that initial capacity of ArrayList is set to smaller than that actually needed, and in some cases, it isn't set at all.
Additionally, while LineString and MultiPoint use assertions for validating parameters, but Polygon doesn't.

I created this issue for fix it.

Thank you.