Don't include execnodes.h in replication/conflict.h

... which silently propagates a lot of headers into many places
via pgstat.h, as evidenced by the variety of headers that this patch
needs to add to seemingly random places.  Add a minimum of typedefs to
conflict.h to be able to remove execnodes.h, and fix the fallout.

Backpatch to 18, where conflict.h first appeared.

Discussion: https://postgr.es/m/202509191927.uj2ijwmho7nv@alvherre.pgsql

src/backend/access/transam/multixact.c

@@ -79,6 +79,7 @@
 #include "pg_trace.h"
 #include "pgstat.h"
 #include "postmaster/autovacuum.h"
+#include "storage/condition_variable.h"
 #include "storage/pmsignal.h"
 #include "storage/proc.h"
 #include "storage/procarray.h"

src/backend/access/transam/xlogrecovery.c

@@ -45,6 +45,7 @@
 #include "commands/tablespace.h"
 #include "common/file_utils.h"
 #include "miscadmin.h"
+#include "nodes/miscnodes.h"
 #include "pgstat.h"
 #include "postmaster/bgwriter.h"
 #include "postmaster/startup.h"

src/backend/storage/ipc/waiteventset.c

@@ -67,6 +67,7 @@
 #include "libpq/pqsignal.h"
 #include "miscadmin.h"
 #include "pgstat.h"
+#include "port/atomics.h"
 #include "portability/instr_time.h"
 #include "postmaster/postmaster.h"
 #include "storage/fd.h"

src/backend/utils/activity/pgstat_backend.c

@@ -25,6 +25,7 @@
 #include "postgres.h"
 
 #include "access/xlog.h"
+#include "executor/instrument.h"
 #include "storage/bufmgr.h"
 #include "storage/proc.h"
 #include "storage/procarray.h"

src/include/pgstat.h

@@ -11,6 +11,7 @@
 #ifndef PGSTAT_H
 #define PGSTAT_H
 
+#include "access/transam.h"		/* for FullTransactionId */
 #include "datatype/timestamp.h"
 #include "portability/instr_time.h"
 #include "postmaster/pgarch.h"	/* for MAX_XFN_CHARS */

src/include/replication/conflict.h

@@ -9,9 +9,16 @@
 #ifndef CONFLICT_H
 #define CONFLICT_H
 
-#include "nodes/execnodes.h"
+#include "access/xlogdefs.h"
+#include "nodes/pg_list.h"
 #include "utils/timestamp.h"
 
+/* Avoid including execnodes.h here */
+typedef struct EState EState;
+typedef struct ResultRelInfo ResultRelInfo;
+typedef struct TupleTableSlot TupleTableSlot;
+
+
 /*
  * Conflict types that could occur while applying remote changes.
  *