[zerocopy] Add byteorder/native conversions
[zerocopy] Add byteorder/native conversions

- Add fallible and infallible conversions between byteorder and native
  types
- Add fallible and infallible conversions between byteorder types

Change-Id: I3284307158424e6728df903a0ae9f9d356d30f3c
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/506999
Reviewed-by: Adam Perry <2758bbec8dee427942fa5466889635696219b7ab@google.com>
Commit-Queue: Joshua Liebow-Feeser <234d196e9838c6e234061de31cd689c2a331d758@google.com>

google/zerocopy,google/zerocopy