For 11 only, put back heap_expand_tuple to GetTupleForTrigger().

For 11 only, put back heap_expand_tuple to GetTupleForTrigger().

This is not necessary anymore after 297d627e, but extensions that have
not been recompiled after the fix will not use the new definition of
heap_getattr(). While recompiling those extensions is obviously the
suggested course, it's cheap enough to retain the expansion in
GetTupleForTrigger().

Per suggestion from Andrew Gierth.

Discussion: 87va1x43ot.fsf@news-spur.riddles.org.uk