Progress reporting: also report the primary action output

While reporting an origin target with action number within that
target describes an action uniquely in a way meaningful to the
user, it might not always be eay to unserstand which precise action
is currently running. For example, for a library with many source
files, we have a target generating a large number of actions and
the association of source file to action number requires detailled
knowledge of the build description. The name of the primary ouput
of that action, on the other hand immediately identifies the file
that is compiled. Therefore, report this as well.

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