Avoid ThreadLocal memory leak in JoinPointImpl

Avoid ThreadLocal memory leak in JoinPointImpl

according to https://rules.sonarsource.com/java/tag/leak/RSPEC-5164/.
Now, there no longer is a thread-local stack of AroundClosure instances,
but rather a list of them, which can only grow but never shrink.
Instead, we now have a thread-local (integer) list index, for every
thread being initialised with pointing to the last element. I.e., every
thread can unwind by decrementing the index while proceeding,
independently of other threads.

A positive side effect is that this approach also works for long-lived
threads from thread pools, used by executor services. Hence, test
Bugs199Tests.testAsyncProceedNestedAroundAdviceThreadPool_gh128, which
was previously commented out, has been activated and passes, see #141.

I am not sure if this brings @AspectJ style, non-inlined, nested around
advice execution functionally on par with native ones, but at least for
current scenarios it seems to work.

Fixes #288, #141.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>