Tmf: Add the experiment type to the trace type extension point

Tmf: Add the experiment type to the trace type extension point

This will allow to define experiment types using the same extension point as
the trace type, so the same handlers and contribution items can be used.

Change-Id: I8ae7da262e2a1e7eab78cf9e763f1fbc0babf5fb
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Reviewed-on: https://git.eclipse.org/r/13787
Tested-by: Hudson CI
Reviewed-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
IP-Clean: Bernd Hufmann <bernd.hufmann@ericsson.com>
Tested-by: Bernd Hufmann <bernd.hufmann@ericsson.com>