BUGFIX: Fix name-based way fragmentation in transportation_name (#1295)

I discovered this bug while investigating issues with the updates process related to #1190 #1292, and #814.

The `transportation_name` layer produces slightly different `tags` hstore values in the `osm_transportation_name_linestring` table during the initial import versus when running an update.  As currently written, the import code produces null-value keys in the `tags` column, while the update code suppresses them.  This PR removes that difference and makes the import code use same method that is currently used in the update code.

With a test case I've written, the import code produces a tags hstore that looks like this:
`"name"=>"OpenMapTiles Secondary 2", "name:de"=>NULL, "name:en"=>NULL, "name_int"=>"OpenMapTiles Secondary 2", "name:latin"=>"OpenMapTiles Secondary 2"`

...while the update code produces a tags hstore that looks like this:

`"name"=>"OpenMapTiles Secondary 2", "name_int"=>"OpenMapTiles Secondary 2", "name:latin"=>"OpenMapTiles Secondary 2"`

Note the missing NULL values.

This bug causes a small amount of space wastage after an update is run, because the update matching code detects the `tags` value as different, resulting in a duplicate copy of the tags value if that row is updated.  This causes duplicate objects and breaks GROUP BY clauses that expect to group same-tagged features together.  I've tested this by inspection of a generated mbtiles, database spot checks, and the unit test code included in this PR.

layers/transportation_name/transportation_name.sql

@@ -28,9 +28,9 @@ CREATE OR REPLACE FUNCTION layer_transportation_name(bbox geometry, zoom_level i
 AS
 $$
 SELECT geometry,
-       name,
-       COALESCE(name_en, name) AS name_en,
-       COALESCE(name_de, name, name_en) AS name_de,
+       tags->'name' AS name,
+       COALESCE(tags->'name:en', tags->'name') AS name_en,
+       COALESCE(tags->'name:de', tags->'name', tags->'name:en') AS name_de,
        tags,
        ref,
        NULLIF(LENGTH(ref), 0) AS ref_length,
@@ -93,9 +93,6 @@ FROM (
 
          -- etldoc: osm_transportation_name_linestring ->  layer_transportation_name:z12
          SELECT geometry,
-                name,
-                name_en,
-                name_de,
                 "tags",
                 ref,
                 highway,
@@ -109,7 +106,7 @@ FROM (
                 indoor
          FROM osm_transportation_name_linestring
          WHERE zoom_level = 12
-           AND LineLabel(zoom_level, COALESCE(name, ref), geometry)
+           AND LineLabel(zoom_level, COALESCE(tags->'name', ref), geometry)
            AND NOT highway_is_link(highway)
            AND
                CASE WHEN highway_class(highway, NULL::text, NULL::text) NOT IN ('path', 'minor') THEN TRUE
@@ -120,9 +117,6 @@ FROM (
 
          -- etldoc: osm_transportation_name_linestring ->  layer_transportation_name:z13
          SELECT geometry,
-                name,
-                name_en,
-                name_de,
                 "tags",
                 ref,
                 highway,
@@ -136,11 +130,11 @@ FROM (
                 indoor
          FROM osm_transportation_name_linestring
          WHERE zoom_level = 13
-           AND LineLabel(zoom_level, COALESCE(name, ref), geometry)
+           AND LineLabel(zoom_level, COALESCE(tags->'name', ref), geometry)
            AND
                CASE WHEN highway <> 'path' THEN TRUE
                     WHEN highway = 'path' AND (
-                                                   name <> ''
+                                                   tags->'name' <> ''
                                                 OR network IS NOT NULL
                                                 OR sac_scale <> ''
                                                 OR route_rank <= 2
@@ -151,9 +145,6 @@ FROM (
 
          -- etldoc: osm_transportation_name_linestring ->  layer_transportation_name:z14_
          SELECT geometry,
-                name,
-                name_en,
-                name_de,
                 "tags",
                 ref,
                 highway,
@@ -172,11 +163,8 @@ FROM (
          -- etldoc: osm_highway_point ->  layer_transportation_name:z10
          SELECT
 		p.geometry,
-                p.name,
-                p.name_en,
-                p.name_de,
                 p.tags,
-                p.tags->'ref',
+                p.ref,
                 (
                   SELECT highest_highway(l.tags->'highway')
                     FROM osm_highway_linestring l