[#2812] Ensure we call checkForSharableAnnotation in all constructors of ByteToMessageCodec

Motivation:

ByteToMessageCodec miss to check for @Sharable annotation in one of its constructors.

Modifications:

Ensure we call checkForSharableAnnotation in all constructors.

Result:

After your change, what will change.
Move duplicated code into CodecUtil

Motivation:

We have some duplicated code that can be reused.

Modifications:

Create package private class called CodecUtil that now contains the shared code / helper method.

Result:

Less code-duplication
Add io.netty.noJdkZlibEncoder system property

Related issue: #2821

Motivation:

There's no way for a user to change the default ZlibEncoder
implementation.

It is already possible to change the default ZlibDecoder implementation.

Modification:

Add a new system property 'io.netty.noJdkZlibEncoder'.

Result:

A user can disable JDK ZlibEncoder, just like he or she can disable JDK
ZlibDecoder.
Check noJdkZlibEncoder before comparing other parameters

.. for consistency
[#2823] Writing DefaultFileRegion with EpollSocketChannel may cause hang

Motivation:

In EpollSocketchannel.doWriteFileRegion(...) we need to make sure we write until sendFile(...) returns either 0 or all is written. Otherwise we may not get notified once the Channel is writable again.

This is the case as we use EPOLL_ET.

Modifications:

Always write until either sendFile returns 0 or all is written.

Result:

No more hangs when writing DefaultFileRegion can happen.