Add simplified water materialized views

Move materialized view creation from the tools repo.
This should be coordinated with
  openmaptiles/openmaptiles-tools#115

This PR is similar to openmaptiles#740

layers/water/water.sql

@@ -1,3 +1,44 @@
+-- This statement can be deleted after the water importer image stops creating this object as a table
+DO $$ BEGIN DROP TABLE IF EXISTS osm_ocean_polygon_gen1 CASCADE; EXCEPTION WHEN wrong_object_type THEN END; $$ language 'plpgsql';
+-- etldoc: osm_ocean_polygon -> osm_ocean_polygon_gen1
+DROP MATERIALIZED VIEW IF EXISTS osm_ocean_polygon_gen1 CASCADE;
+CREATE MATERIALIZED VIEW osm_ocean_polygon_gen1 AS (
+  SELECT ST_Simplify(geometry, 20) AS geometry FROM osm_ocean_polygon
+) /* DELAY_MATERIALIZED_VIEW_CREATION */ ;
+CREATE INDEX IF NOT EXISTS osm_ocean_polygon_gen1_idx ON osm_ocean_polygon_gen1 USING gist (geometry);
+
+
+-- This statement can be deleted after the water importer image stops creating this object as a table
+DO $$ BEGIN DROP TABLE IF EXISTS osm_ocean_polygon_gen2 CASCADE; EXCEPTION WHEN wrong_object_type THEN END; $$ language 'plpgsql';
+-- etldoc: osm_ocean_polygon -> osm_ocean_polygon_gen2
+DROP MATERIALIZED VIEW IF EXISTS osm_ocean_polygon_gen2 CASCADE;
+CREATE MATERIALIZED VIEW osm_ocean_polygon_gen2 AS (
+  SELECT ST_Simplify(geometry, 40) AS geometry FROM osm_ocean_polygon
+) /* DELAY_MATERIALIZED_VIEW_CREATION */ ;
+CREATE INDEX IF NOT EXISTS osm_ocean_polygon_gen2_idx ON osm_ocean_polygon_gen2 USING gist (geometry);
+
+
+-- This statement can be deleted after the water importer image stops creating this object as a table
+DO $$ BEGIN DROP TABLE IF EXISTS osm_ocean_polygon_gen3 CASCADE; EXCEPTION WHEN wrong_object_type THEN END; $$ language 'plpgsql';
+-- etldoc: osm_ocean_polygon -> osm_ocean_polygon_gen3
+DROP MATERIALIZED VIEW IF EXISTS osm_ocean_polygon_gen3 CASCADE;
+CREATE MATERIALIZED VIEW osm_ocean_polygon_gen3 AS (
+  SELECT ST_Simplify(geometry, 80) AS geometry FROM osm_ocean_polygon
+) /* DELAY_MATERIALIZED_VIEW_CREATION */ ;
+CREATE INDEX IF NOT EXISTS osm_ocean_polygon_gen3_idx ON osm_ocean_polygon_gen3 USING gist (geometry);
+
+
+-- This statement can be deleted after the water importer image stops creating this object as a table
+DO $$ BEGIN DROP TABLE IF EXISTS osm_ocean_polygon_gen4 CASCADE; EXCEPTION WHEN wrong_object_type THEN END; $$ language 'plpgsql';
+-- etldoc: osm_ocean_polygon -> osm_ocean_polygon_gen4
+DROP MATERIALIZED VIEW IF EXISTS osm_ocean_polygon_gen4 CASCADE;
+CREATE MATERIALIZED VIEW osm_ocean_polygon_gen4 AS (
+  SELECT ST_Simplify(geometry, 160) AS geometry FROM osm_ocean_polygon
+) /* DELAY_MATERIALIZED_VIEW_CREATION */ ;
+CREATE INDEX IF NOT EXISTS osm_ocean_polygon_gen4_idx ON osm_ocean_polygon_gen4 USING gist (geometry);
+
+
+
 CREATE OR REPLACE FUNCTION water_class(waterway TEXT) RETURNS TEXT AS $$
     SELECT CASE
            WHEN waterway='' THEN 'lake'