Improve native code's performance when writing to HDFS

For reads, we introduced direct buffers in order to more efficiently communicate between the JVM and the native code, and we have readDirect and pReadDirect in hdfs.c implemented.

Writes on the other hand still use the putByteArrayRegion call, which results in a copy of the buffer in memory.

This Jira is to explore what has to be done in order to start to use direct buffers.
A short initial list I see at the moment:

• add a new StreamCapability for streams wanting to support writes via direct buffer
  - implement this capability in the DFSOutputStream and DFSStripedOutputStream
• implement a writeDirect method on the native side

fuse_dfs can benefit from this.