message: [FlexBuffers][Java] Cache size of Sized objects in FlexBuffers
  In my benchmarks it shows deserialization performance improvements of
  around 7%
diff: @@ -635,12 +635,16 @@ public class FlexBuffers {
  // Stores size in `byte_width_` bytes before end position.
  private static abstract class Sized extends Object {
  +
  + private final int size;
  +
  Sized(ByteBuffer buff, int end, int byteWidth) {
  super(buff, end, byteWidth);
  + size = readInt(bb, end - byteWidth, byteWidth);
  }
  public int size() {
  - return readInt(bb, end - byteWidth, byteWidth);
  + return size;
  }
  }
  