Fix access to no-longer-open relcache entry in logical-rep worker.

If we redirected a replicated tuple operation into a partition child
table, and then tried to fire AFTER triggers for that event, the
relation cache entry for the child table was already closed.  This has
no visible ill effects as long as the entry is still there and still
valid, but an unluckily-timed cache flush could result in a crash or
other misbehavior.

To fix, postpone the ExecCleanupTupleRouting call (which is what
closes the child table) until after we've fired triggers.  This
requires a bit of refactoring so that the cleanup function can
have access to the necessary state.

In HEAD, I took the opportunity to simplify some of worker.c's
function APIs based on use of the new ApplyExecutionData struct.
However, it doesn't seem safe/practical to back-patch that aspect,
at least not without a lot of analysis of possible interactions
with a04daa97.

In passing, add an Assert to afterTriggerInvokeEvents to catch
such cases.  This seems worthwhile because we've grown a number
of fairly unstructured ways of calling AfterTriggerEndQuery.

Back-patch to v13, where worker.c grew the ability to deal with
partitioned target tables.

Discussion: https://postgr.es/m/3382681.1621381328@sss.pgh.pa.us

src/backend/commands/trigger.c

@@ -4219,6 +4219,8 @@ afterTriggerInvokeEvents(AfterTriggerEventList *events,
 				{
 					rInfo = ExecGetTriggerResultRel(estate, evtshared->ats_relid);
 					rel = rInfo->ri_RelationDesc;
+					/* Catch calls with insufficient relcache refcounting */
+					Assert(!RelationHasReferenceCountZero(rel));
 					trigdesc = rInfo->ri_TrigDesc;
 					finfo = rInfo->ri_TrigFunctions;
 					instr = rInfo->ri_TrigInstrument;