Add support for Bus Rapid Transit (highway=busway) (openmaptiles#1271)

This PR adds support for bus rapid transit (BRT) systems, mapped with the [approved tag](https://wiki.openstreetmap.org/wiki/Proposed_features/Tag:highway%3Dbusway) `highway=busway`. BRT systems commonly appear in maps that also show light rail.  Below are two examples of BRT in such maps.

![image (1)](https://user-images.githubusercontent.com/3254090/138018375-ac1f60c3-8059-4f95-bf1d-a659ca0c0103.png)
![image](https://user-images.githubusercontent.com/3254090/138018376-f809aeb3-17ba-495e-b33c-9fe54a0fa840.png)

Since BRT is equivalent in nature to light rail systems, this PR matches the zoom level of light rail, which is rendered at zoom 11+.  BRT systems are relatively uncommon, so adding this support should have negligible impact on tile size.

Below is a data rendering of [a BRT system](https://www.openstreetmap.org/relation/4051383#map=12/40.4068/-79.8646) in Pittsburgh, Pennsylvania.

![image](https://user-images.githubusercontent.com/3254090/138021552-ce974f2f-cfbd-42a0-9848-42ed44da453e.png)

layers/transportation/class.sql

@@ -66,7 +66,8 @@ SELECT CASE
                (
                 'motorway', 'trunk', 'primary', 'secondary', 'tertiary', 'raceway',
                 'motorway_construction', 'trunk_construction', 'primary_construction',
-                'secondary_construction', 'tertiary_construction', 'raceway_construction'
+                'secondary_construction', 'tertiary_construction', 'raceway_construction',
+                'busway'
                ) THEN TRUE --includes ramps
            ELSE FALSE
        END

layers/transportation/mapping.yaml

@@ -45,7 +45,7 @@ generalized_tables:
 # etldoc: osm_highway_linestring -> osm_highway_linestring_gen_z11
   highway_linestring_gen_z11:
     source: highway_linestring
-    sql_filter: (highway IN ('motorway', 'trunk', 'primary', 'secondary', 'tertiary', 'motorway_link', 'trunk_link', 'primary_link', 'secondary_link', 'tertiary_link') OR highway = 'construction' AND construction IN ('motorway', 'trunk', 'primary', 'secondary', 'tertiary', 'motorway_link', 'trunk_link', 'primary_link', 'secondary_link', 'tertiary_link')) AND NOT is_area AND ST_IsValid(geometry)
+    sql_filter: (highway IN ('motorway', 'trunk', 'primary', 'secondary', 'tertiary', 'motorway_link', 'trunk_link', 'primary_link', 'secondary_link', 'tertiary_link', 'busway') OR highway = 'construction' AND construction IN ('motorway', 'trunk', 'primary', 'secondary', 'tertiary', 'motorway_link', 'trunk_link', 'primary_link', 'secondary_link', 'tertiary_link', 'busway')) AND NOT is_area AND ST_IsValid(geometry)
     tolerance: ZRES12
 
 name_field: &name
@@ -227,6 +227,7 @@ tables:
       - service
       - track
       - raceway
+      - busway
       - construction
       public_transport:
       - platform

layers/transportation/transportation.yaml

@@ -45,6 +45,8 @@ layer:
           highway: track
         raceway:
           highway: raceway
+        busway:
+          highway: busway
         motorway_construction:
           __AND__:
             highway: construction

layers/transportation/update_transportation_merge.sql

@@ -61,8 +61,8 @@ SELECT ST_Simplify(geometry, ZRes(12)) AS geometry,
        toll,
        layer
 FROM osm_transportation_merge_linestring_gen_z11
-WHERE highway NOT IN ('tertiary', 'tertiary_link')
-      AND construction NOT IN ('tertiary', 'tertiary_link')
+WHERE highway NOT IN ('tertiary', 'tertiary_link', 'busway')
+      AND construction NOT IN ('tertiary', 'tertiary_link', 'busway')
     ) /* DELAY_MATERIALIZED_VIEW_CREATION */;
 CREATE INDEX IF NOT EXISTS osm_transportation_merge_linestring_gen_z10_geometry_idx
     ON osm_transportation_merge_linestring_gen_z10 USING gist (geometry);