Spring Increase StreamUtils.BUFFER_SIZE to 8192

This aligns the buffer size used in StreamUtils with the buffer sized used throughout the JDK (see InputStream, BufferedInputStream, Files).

Comment From: kilink

FYI, it's also the buffer size used in Guava and Apache Commons.

Comment From: bclozel

Thanks for your first contribution @kilink , this will be in the next 6.0.0 milestone.