__Motivation__
In order to migrate all codec incrementally to use `Buffer`, we need a version of `ByteToMessageDecoder` that uses `Buffer`.
__Modification__
- Added the new version of `ByteToMessageDecoder` with a new name so that both old and new version can co-exist and we can incrementally migrate all codecs
- Migrated `FixedLengthFrameDecoder` as it was simple and used in tests.
__Result__
We have the basic building block to start migrating all codecs to the new `Buffer` API.
29cae0445a