Split function definitions out of system_views.sql into a new file.

Invent system_functions.sql to carry the function definitions that
were formerly in system_views.sql.  The function definitions were
already a quarter of the file and are about to be more, so it seems
appropriate to give them their own home.

In passing, fix an oversight in dfb75e47: it neglected to call
check_input() for system_constraints.sql.

Discussion: https://postgr.es/m/3956760.1618529139@sss.pgh.pa.us

src/backend/catalog/Makefile

@@ -122,6 +122,7 @@ $(top_builddir)/src/include/catalog/header-stamp: bki-stamp
 install-data: bki-stamp installdirs
 	$(INSTALL_DATA) $(call vpathsearch,postgres.bki) '$(DESTDIR)$(datadir)/postgres.bki'
 	$(INSTALL_DATA) $(call vpathsearch,system_constraints.sql) '$(DESTDIR)$(datadir)/system_constraints.sql'
+	$(INSTALL_DATA) $(srcdir)/system_functions.sql '$(DESTDIR)$(datadir)/system_functions.sql'
 	$(INSTALL_DATA) $(srcdir)/system_views.sql '$(DESTDIR)$(datadir)/system_views.sql'
 	$(INSTALL_DATA) $(srcdir)/information_schema.sql '$(DESTDIR)$(datadir)/information_schema.sql'
 	$(INSTALL_DATA) $(srcdir)/sql_features.txt '$(DESTDIR)$(datadir)/sql_features.txt'
@@ -131,7 +132,7 @@ installdirs:
 
 .PHONY: uninstall-data
 uninstall-data:
-	rm -f $(addprefix '$(DESTDIR)$(datadir)'/, postgres.bki system_constraints.sql system_views.sql information_schema.sql sql_features.txt)
+	rm -f $(addprefix '$(DESTDIR)$(datadir)'/, postgres.bki system_constraints.sql system_functions.sql system_views.sql information_schema.sql sql_features.txt)
 
 # postgres.bki, system_constraints.sql, and the generated headers are
 # in the distribution tarball, so they are not cleaned here.

src/bin/initdb/initdb.c

@@ -160,6 +160,7 @@ static char *dictionary_file;
 static char *info_schema_file;
 static char *features_file;
 static char *system_constraints_file;
+static char *system_functions_file;
 static char *system_views_file;
 static bool success = false;
 static bool made_new_pgdata = false;
@@ -2506,6 +2507,7 @@ setup_data_file_paths(void)
 	set_input(&info_schema_file, "information_schema.sql");
 	set_input(&features_file, "sql_features.txt");
 	set_input(&system_constraints_file, "system_constraints.sql");
+	set_input(&system_functions_file, "system_functions.sql");
 	set_input(&system_views_file, "system_views.sql");
 
 	if (show_setting || debug)
@@ -2532,6 +2534,8 @@ setup_data_file_paths(void)
 	check_input(dictionary_file);
 	check_input(info_schema_file);
 	check_input(features_file);
+	check_input(system_constraints_file);
+	check_input(system_functions_file);
 	check_input(system_views_file);
 }
 
@@ -2869,6 +2873,8 @@ initialize_data_directory(void)
 
 	setup_run_file(cmdfd, system_constraints_file);
 
+	setup_run_file(cmdfd, system_functions_file);
+
 	setup_depend(cmdfd);
 
 	/*