add additional (debug) logging to AbstractStreamWriterGenerator

add additional (debug) logging to AbstractStreamWriterGenerator

* LOG.debug() in generateSerializer() to see if in a load test
scenario that ever gets called twice for the same type (it should not)
due to a concurrency bug I'm not seeing.

* reduce the only other LOG.debug() in that class to trace()
because that one will happen more often (constantly?) and make it hard
to see the other one.

* log onBindingRuntimeContextUpdated() on the off chance
that changing the BindingRuntimeContext somehow could cause this
suspected concurrency issue.

* log constructor to better understand the lifecycle of
AbstractStreamWriterGenerator in production.

* add Guava Cache removalListener with logging to see if this is caused
by eviction by GC due to .weakKeys() - ACK to tpantelis for this hunch.

JIRA: MDSAL-213
Change-Id: I2416131fe140ee483cc93740480ee0e37f0ce130
Signed-off-by: Michael Vorburger <vorburger@redhat.com>