Move aboriginal lands boundaries to boundary layer (#1604)

This PR adds indigenous lands to the `boundary` layer by adding new area features for these objects, along with generalization up to z4. It borrows heavily from the technical processing chain of the `park` layer.

I added new `class`, `name`, and `name:xx` attributes to the boundary layer, in order to support the new area features. Should we (or someone extending this schema) come up with new objects to place in the boundary layer in the future, `class` would support additional categories.

layers/park/park.sql

@@ -26,12 +26,11 @@ SELECT osm_id,
 FROM (
          SELECT osm_id,
                 geometry,
-                CASE WHEN boundary='aboriginal_lands' THEN 'aboriginal_lands'
-                     ELSE COALESCE(
-                          LOWER(REPLACE(NULLIF(protection_title, ''), ' ', '_')),
-                          NULLIF(boundary, ''),
-                          NULLIF(leisure, '')
-                    ) END AS class,
+                COALESCE(
+                    LOWER(REPLACE(NULLIF(protection_title, ''), ' ', '_')),
+                    NULLIF(boundary, ''),
+                    NULLIF(leisure, ''))
+                AS class,
                 name,
                 name_en,
                 name_de,
@@ -46,7 +45,7 @@ FROM (
                          NULL AS name_de,
                          NULL AS tags,
                          NULL AS leisure,
-                         CASE WHEN boundary='aboriginal_lands' THEN boundary END AS boundary,
+                         NULL AS boundary,
                          NULL AS protection_title
                   FROM osm_park_polygon_dissolve_z4
                   WHERE zoom_level = 4