Add cache state to task summaries on real runs (2nd try) (#4393)
This commit threads the itemStatus struct all the way
down to execContext.exec() so we can include it in the run
summaries.
This is a re-implementation of 883d6d4d9f212998869623c25712b5aa3e230871
which had a crucial bug where RestoreOutputs would report a cache hit,
but then _return_ a cache miss value, so the caller (execContext.exec())
would continue executing as if there were a cache miss.
