ARTEMIS-3059 AMQP message reencoding should save creating Netty heap arenas

[franz1981]

https://issues.apache.org/jira/browse/ARTEMIS-3059

[franz1981]

@gemmellr and @clebertsuconic need your review here: I see that we have several parts on the broker that are using pooled heap buffers...

[franz1981]

It doesn't seem enough to save Netty heap arenas to be allocated, see

[gemmellr]

I dont really know much about the brokers pooled netty buffer usages, most of my usage (elsewhere) avoids them. As you say there do look to be others uses besides the one changed here.

[franz1981]

@gemmellr it seems that Netty pooled heap arenas are still allocated, but are empty (that's why they have such small footprint on the screenshot).
This PR is delivering the improvement I was seeking.

I dont really know much about the brokers pooled netty buffer usages, most of my usage (elsewhere) avoids them. As you say there do look to be others uses besides the one changed here.

I see that AMQPMessage::createDeliveryCopy is using it, but probably @clebertsuconic knows about it

[clebertsuconic]

@franz1981 we should probably review and manage those PooledBuffers usage as whole?