Convert semi-colon separated house numbers to a range (#1562)

This PR collapses housenumber values into the form min(housenumber)-max(housenumber) for cases where housenumber is a semi-colon separated list. If the list is all numbers, the bounds are the smallest and largest numbers.  If the list includes non-numeric characters, it falls back to the first and last values in the list.

layers/housenumber/housenumber_display.sql

@@ -0,0 +1,20 @@
+CREATE OR REPLACE FUNCTION display_housenumber_nonnumeric(raw_housenumber text)
+RETURNS text AS $$
+  -- Find the position of the semicolon in the input string
+  -- and extract the first and last value
+  SELECT substring(raw_housenumber from 1 for position(';' in raw_housenumber) - 1)
+         || '–'
+         || substring(raw_housenumber from position(';' in raw_housenumber) + 1);
+$$ LANGUAGE SQL IMMUTABLE;
+
+
+CREATE OR REPLACE FUNCTION display_housenumber(raw_housenumber text)
+RETURNS text AS $$
+  SELECT CASE
+    WHEN raw_housenumber !~ ';' THEN raw_housenumber
+    WHEN raw_housenumber ~ '[^0-9;]' THEN display_housenumber_nonnumeric(raw_housenumber)
+    ELSE
+      (SELECT min(value)::text || '–' || max(value)::text
+       FROM unnest(string_to_array(raw_housenumber, ';')::int[]) AS value)
+  END
+$$ LANGUAGE SQL IMMUTABLE;