Additional unicode primitive functions.

Introduce unicode_version(), icu_unicode_version(), and
unicode_assigned().

The latter requires introducing a new lookup table for the Unicode
General Category, which is generated along with the other Unicode
lookup tables.

Discussion: https://postgr.es/m/CA+TgmoYzYR-yhU6k1XFCADeyj=Oyz2PkVsa3iKv+keM8wp-F_A@mail.gmail.com
Reviewed-by: Peter Eisentraut

src/common/unicode/generate-unicode_version.pl

@@ -0,0 +1,46 @@
+#!/usr/bin/perl
+#
+# Generate header file with Unicode version used by Postgres.
+#
+# Output: unicode_version.h
+#
+# Copyright (c) 2000-2023, PostgreSQL Global Development Group
+
+use strict;
+use warnings;
+use Getopt::Long;
+
+use FindBin;
+use lib "$FindBin::RealBin/../../tools/";
+
+my $output_path = '.';
+my $version_str = undef;
+
+GetOptions('outdir:s' => \$output_path, 'version:s' => \$version_str);
+
+my @version_parts = split /\./, $version_str;
+
+my $unicode_version_str = sprintf "%d.%d", $version_parts[0], $version_parts[1];
+
+my $output_file = "$output_path/unicode_version.h";
+
+# Start writing out the output files
+open my $OT, '>', $output_file
+  or die "Could not open output file $output_file: $!\n";
+
+print $OT <<HEADER;
+/*-------------------------------------------------------------------------
+ *
+ * unicode_version.h
+ *	  Unicode version used by Postgres.
+ *
+ * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/common/unicode_version.h
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#define PG_UNICODE_VERSION		"$unicode_version_str"
+HEADER