FileHandle is not streaming the response to a File

[rjrudin]

Found this while analyzing something else with @ehennum - I believe it's expected that when using a FileHandle with something like RowManager.resultDoc, the response from ML should be streamed to the given File. Instead, the entire response is being read in as a String and then written to the File, which is much more expensive.

@ehennum confirmed that this is not specific to RowManager either, it's generic to FileHandle - com/marklogic/client/impl/OkHttpServices.java#5364-5373

[ehennum]

The implementation of OKHttpServices should probably use NIO similar to the ReadHandle implementation (though that might use CharBuffer with OutputStreamWriter)