Fix negative feature IDs (#1185)

This PR removes the possibility of negative feature IDs for the `aerodrome_label` layer by defining the feature as the absolute value of the OSM id (imposm maps relations with negative numbers).  There is a very unlikely  scenario in which a relation and a way have the same ID (and are also in the same tile), however, unique IDs are not a strict requirement of MVT.

Noted in:
https://github.com/openmaptiles/openmaptiles/pull/1176#issuecomment-902503655

Positive feature ID for Quonset State Airport, which is mapped as a relation:
![image](https://user-images.githubusercontent.com/3254090/130232322-c797d491-ece9-4889-9695-ffb6f3ac011f.png)

layers/aerodrome_label/aerodrome_label.sql

@@ -5,7 +5,7 @@ CREATE OR REPLACE FUNCTION layer_aerodrome_label(bbox geometry,
                                                  zoom_level integer)
     RETURNS TABLE
             (
-                osm_id   bigint,
+                id       bigint,
                 geometry geometry,
                 name     text,
                 name_en  text,
@@ -21,7 +21,7 @@ AS
 $$
 SELECT
     -- etldoc: osm_aerodrome_label_point -> layer_aerodrome_label:z10_
-    osm_id,
+    ABS(osm_id) AS id, -- mvt feature IDs can't be negative
     geometry,
     name,
     COALESCE(NULLIF(name_en, ''), name) AS name_en,