Custom reloptions for table AM

Let table AM define custom reloptions for its tables.  This allows to
specify AM-specific parameters by WITH clause when creating a table.

The code may use some parts from prior work by Hao Wu.

Discussion: https://postgr.es/m/CAPpHfdurb9ycV8udYqM%3Do0sPS66PJ4RCBM1g-bBpvzUfogY0EA%40mail.gmail.com
Discussion: https://postgr.es/m/AMUA1wBBBxfc3tKRLLdU64rb.1.1683276279979.Hmail.wuhao%40hashdata.cn
Reviewed-by: Reviewed-by: Pavel Borisov, Matthias van de Meent

src/backend/utils/cache/relcache.c

@@ -33,6 +33,7 @@
 #include "access/htup_details.h"
 #include "access/multixact.h"
 #include "access/parallel.h"
+#include "access/relation.h"
 #include "access/reloptions.h"
 #include "access/sysattr.h"
 #include "access/table.h"
@@ -464,6 +465,7 @@ RelationParseRelOptions(Relation relation, HeapTuple tuple)
 {
 	bytea	   *options;
 	amoptions_function amoptsfn;
+	const TableAmRoutine *tableam = NULL;
 
 	relation->rd_options = NULL;
 
@@ -478,6 +480,7 @@ RelationParseRelOptions(Relation relation, HeapTuple tuple)
 		case RELKIND_VIEW:
 		case RELKIND_MATVIEW:
 		case RELKIND_PARTITIONED_TABLE:
+			tableam = relation->rd_tableam;
 			amoptsfn = NULL;
 			break;
 		case RELKIND_INDEX:
@@ -493,7 +496,8 @@ RelationParseRelOptions(Relation relation, HeapTuple tuple)
 	 * we might not have any other for pg_class yet (consider executing this
 	 * code for pg_class itself)
 	 */
-	options = extractRelOptions(tuple, GetPgClassDescriptor(), amoptsfn);
+	options = extractRelOptions(tuple, GetPgClassDescriptor(),
+								tableam, amoptsfn);
 
 	/*
 	 * Copy parsed data into CacheMemoryContext.  To guard against the