Move inheritance expansion code into its own file

This commit moves expand_inherited_tables and underlings from
optimizer/prep/prepunionc.c to optimizer/utils/inherit.c.
Also, all of the AppendRelInfo-based expression manipulation routines
are moved to optimizer/utils/appendinfo.c.

No functional code changes.  One exception is the introduction of
make_append_rel_info, but that's still just moving around code.

Also, stop including <limits.h> in prepunion.c, which no longer needs
it since 3fc6e2d7f5.  I (Álvaro) noticed this because Amit was copying
that to inherit.c, which likewise doesn't need it.

Author: Amit Langote
Discussion: https://postgr.es/m/3be67028-a00a-502c-199a-da00eec8fb6e@lab.ntt.co.jp

src/include/optimizer/appendinfo.h

@@ -0,0 +1,42 @@
+/*-------------------------------------------------------------------------
+ *
+ * appendinfo.h
+ *	  Routines for mapping expressions between append rel parent(s) and
+ *	  children
+ *
+ * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/optimizer/appendinfo.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef APPENDINFO_H
+#define APPENDINFO_H
+
+#include "nodes/plannodes.h"
+#include "nodes/relation.h"
+#include "utils/relcache.h"
+
+extern AppendRelInfo *make_append_rel_info(Relation parentrel,
+					 Relation childrel,
+					 Index parentRTindex, Index childRTindex);
+extern Bitmapset *translate_col_privs(const Bitmapset *parent_privs,
+					List *translated_vars);
+extern Node *adjust_appendrel_attrs(PlannerInfo *root, Node *node,
+					   int nappinfos, AppendRelInfo **appinfos);
+
+extern Node *adjust_appendrel_attrs_multilevel(PlannerInfo *root, Node *node,
+								  Relids child_relids,
+								  Relids top_parent_relids);
+
+extern AppendRelInfo **find_appinfos_by_relids(PlannerInfo *root,
+						Relids relids, int *nappinfos);
+
+extern SpecialJoinInfo *build_child_join_sjinfo(PlannerInfo *root,
+						SpecialJoinInfo *parent_sjinfo,
+						Relids left_relids, Relids right_relids);
+extern Relids adjust_child_relids_multilevel(PlannerInfo *root, Relids relids,
+							   Relids child_relids, Relids top_parent_relids);
+
+#endif							/* APPENDINFO_H */

src/include/optimizer/inherit.h

@@ -0,0 +1,22 @@
+/*-------------------------------------------------------------------------
+ *
+ * inherit.h
+ *	  prototypes for inherit.c.
+ *
+ *
+ * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/optimizer/inherit.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef INHERIT_H
+#define INHERIT_H
+
+#include "nodes/relation.h"
+
+
+extern void expand_inherited_tables(PlannerInfo *root);
+
+#endif							/* INHERIT_H */

src/include/optimizer/prep.h

@@ -47,22 +47,4 @@ extern PlanRowMark *get_plan_rowmark(List *rowmarks, Index rtindex);
  */
 extern RelOptInfo *plan_set_operations(PlannerInfo *root);
 
-extern void expand_inherited_tables(PlannerInfo *root);
-
-extern Node *adjust_appendrel_attrs(PlannerInfo *root, Node *node,
-					   int nappinfos, AppendRelInfo **appinfos);
-
-extern Node *adjust_appendrel_attrs_multilevel(PlannerInfo *root, Node *node,
-								  Relids child_relids,
-								  Relids top_parent_relids);
-
-extern AppendRelInfo **find_appinfos_by_relids(PlannerInfo *root,
-						Relids relids, int *nappinfos);
-
-extern SpecialJoinInfo *build_child_join_sjinfo(PlannerInfo *root,
-						SpecialJoinInfo *parent_sjinfo,
-						Relids left_relids, Relids right_relids);
-extern Relids adjust_child_relids_multilevel(PlannerInfo *root, Relids relids,
-							   Relids child_relids, Relids top_parent_relids);
-
 #endif							/* PREP_H */