ust.core: making some classes final

ust.core: making some classes final

This patch is to make some classes final in ust.core component.
It should be final to improve readability and since you should never
extend it. It also allows the jvm to inline methods and improve
performance.

Change-Id: Ifa5d1e667efb3e18f5cd4a9037082469574c16c6
Signed-off-by: Wassim <wassim.nasrallah.36@gmail.com>
Reviewed-on: https://git.eclipse.org/r/73972
Reviewed-by: Hudson CI
Reviewed-by: Genevieve Bastien <gbastien+lttng@versatic.net>
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>