=sam #12702 Create FsmSimpleRedelivery sample

This one is created instead of the batching pattern of #12702, as suggested by @ktoso in #12702's discussion.
=act #15488 Removed guard around _logLevel

This patch removes a lock around the getter of _logLevel. The setter is
still guarded for consistency. Note that out of thin-air reads, while
not excluded under the current JMM, are forbidden by current hardware.

Signed-off-by: Duarte Nunes <duarte.m.nunes@gmail.com>
Merge pull request #15534 from ktoso/port-simple-fsm-redelivery-sample-ktoso

=sam #12702 Create FsmSimpleRedelivery sample (for validation).
Merge pull request #15546 from ktoso/port-removeGuardOnLoglevelRead-ktoso

=act #15488 Removed guard around _logLevel (for validation)
=doc #15543 link to persistence in java docs should point to java persistence
Merge pull request #15548 from ktoso/doc-fix-java-persistence-link-ktoso

=doc #15543 link to persistence in java docs should point to java persis...
=act #15488 volatile logLevel and Guard => RWGuard for loggers