FormData fromatter is not working correctly and returns an empty FormData object

[JorensM]

The fetch-http-client contentFormatter for FormData is not working correctly. It is doing some operations on the original input and returning a new FormData object. The way it is doing it, it is not actually mapping the original properties to the new object, hence returning an empty FormData object

[JorensM]

Here is a PR #747 fixing this