Ensure HTTP classes don't close streams

Prior to this commit several HTTP classes made use of FileCopyUtils
when reading from or writing to streams. This has the unfortunate
side effect of closing streams that should really be left open.

The problem is particularly noticeable when dealing with a
FormHttpMessageConverter that is writing a multi-part response.

Relevant HTTP classes have now been refactored to make use of a new
StreamUtils class that works in a similar way FileCopyUtils but does
not close streams.

The NonClosingOutputStream class from SimpleStreamingClientHttpRequest
has also been refactored to a StreamUtils method.

Issue: SPR-10095