Improve UrlFormatter

[flobernd]

Improvements to CreateString:

1. The IEnumerable<object> was never matching (except for exact this type). I changed the code to check for IEnumerable instead
2. To support arrays with non-zero lower bounds, I kept the Array special case
3. For performance reasons (saving one iterator instance and being able to use for instead of foreach) I special cased IList

Besides that, I fixed some nullability annotations.

Fixes: elastic/elasticsearch-net#8034

[flobernd]

CI fails for unrelated reasons it seems.