Avoid including commands/dbcommands.h in so many places

This has been done historically because of get_database_name (which
since commit cb98e6fb8f belongs in lsyscache.c/h, so let's move it
there) and get_database_oid (which is in the right place, but whose
declaration should appear in pg_database.h rather than dbcommands.h).
Clean this up.

Also, xlogreader.h and stringinfo.h are no longer needed by dbcommands.h
since commit f1fd515b39, so remove them.

Author: Álvaro Herrera <alvherre@kurilemu.de>
Reviewed-by: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/202508191031.5ipojyuaswzt@alvherre.pgsql

src/backend/access/heap/vacuumlazy.c

@@ -140,7 +140,6 @@
 #include "access/visibilitymap.h"
 #include "access/xloginsert.h"
 #include "catalog/storage.h"
-#include "commands/dbcommands.h"
 #include "commands/progress.h"
 #include "commands/vacuum.h"
 #include "common/int.h"

src/backend/access/transam/multixact.c

@@ -75,7 +75,6 @@
 #include "access/xlog.h"
 #include "access/xloginsert.h"
 #include "access/xlogutils.h"
-#include "commands/dbcommands.h"
 #include "miscadmin.h"
 #include "pg_trace.h"
 #include "pgstat.h"
@@ -85,6 +84,7 @@
 #include "storage/procarray.h"
 #include "utils/guc_hooks.h"
 #include "utils/injection_point.h"
+#include "utils/lsyscache.h"
 #include "utils/memutils.h"
 
 

src/backend/access/transam/varsup.c

@@ -19,11 +19,11 @@
 #include "access/transam.h"
 #include "access/xact.h"
 #include "access/xlogutils.h"
-#include "commands/dbcommands.h"
 #include "miscadmin.h"
 #include "postmaster/autovacuum.h"
 #include "storage/pmsignal.h"
 #include "storage/proc.h"
+#include "utils/lsyscache.h"
 #include "utils/syscache.h"