Represent command completion tags as structs

The backend was using strings to represent command tags and doing string
comparisons in multiple places, but that's slow and unhelpful.  Create a
new command list with a supporting structure to use instead; this is
stored in a tag-list-file that can be tailored to specific purposes with
a caller-definable C macro, similar to what we do for WAL resource
managers.  The first first such uses are a new CommandTag enum and a
CommandTagBehavior struct.

Replace numerous occurrences of char *completionTag with a
QueryCompletion struct so that the code no longer stores information
about completed queries in a cstring.  Only at the last moment, in
EndCommand(), does this get converted to a string.

EventTriggerCacheItem no longer holds an array of palloc’d tag strings
in sorted order, but rather just a Bitmapset over the CommandTags.

Author: Mark Dilger, with unsolicited help from Álvaro Herrera
Reviewed-by: John Naylor, Tom Lane
Discussion: https://postgr.es/m/981A9DB4-3F0C-4DA5-88AD-CB9CFF4D6CAD@enterprisedb.com

contrib/sepgsql/hooks.c

@@ -317,7 +317,7 @@ sepgsql_utility_command(PlannedStmt *pstmt,
 						ParamListInfo params,
 						QueryEnvironment *queryEnv,
 						DestReceiver *dest,
-						char *completionTag)
+						QueryCompletion *qc)
 {
 	Node	   *parsetree = pstmt->utilityStmt;
 	sepgsql_context_info_t saved_context_info = sepgsql_context_info;
@@ -380,11 +380,11 @@ sepgsql_utility_command(PlannedStmt *pstmt,
 		if (next_ProcessUtility_hook)
 			(*next_ProcessUtility_hook) (pstmt, queryString,
 										 context, params, queryEnv,
-										 dest, completionTag);
+										 dest, qc);
 		else
 			standard_ProcessUtility(pstmt, queryString,
 									context, params, queryEnv,
-									dest, completionTag);
+									dest, qc);
 	}
 	PG_FINALLY();
 	{