Add highway=bus_guideway (#1407)

Guided busways (or bus guideways in OSM terminology) are special roadways along which bus operators can travel smoothly at high speeds without steering. These are tagged highway=bus_guideway on OpenStreetMap.

Currently, highway=busway is surfaced in OpenMapTiles as the busway class in the transportation layer, but highway=bus_guideway is not present. These two types of roadways serve generally similar purposes, so it would make sense to have guided busways at the same zoom levels.

layers/transportation/class.sql

@@ -67,7 +67,7 @@ SELECT CASE
                 'motorway', 'trunk', 'primary', 'secondary', 'tertiary', 'raceway',
                 'motorway_construction', 'trunk_construction', 'primary_construction',
                 'secondary_construction', 'tertiary_construction', 'raceway_construction',
-                'busway'
+                'busway', 'bus_guideway'
                ) THEN TRUE --includes ramps
            ELSE FALSE
        END