Pass polygons through if they’re small already

If a polygon is smaller than the largest polygon in our dataset of
simplified polygons then we’re only throwing away useful detail by
simplifying it.

We should still simplify larger polygons as a fallback, to avoid sending
anything to the CBC that we’re not sure it will like.

The thresholds here are low: we can raise them as we test and experiment
more.

Here’s some data about the Flood Warning Service polygons

Percentile | 80% | 90%   | 95%    | 98%     | 99%     | 99.9%
-----------|-----|-------|--------|---------|---------|---------
Point count| 226 | 401.9 | 640.45 | 1015.38 | 1389.07 | 3008.609

Percentile    | 80% | 90%   | 95%    | 98%     | 99%     | 99.9%
--------------|-----|-------|--------|---------|---------|---------
Polygon count |2----|3------|5-------|8--------|10-------|40.469

app/v2/broadcast/post_broadcast.py

@@ -50,6 +50,11 @@ def create_broadcast():
         ] for area in broadcast_json['areas']
     ))))
 
+    if len(polygons) > 12 or polygons.point_count > 250:
+        simple_polygons = polygons.smooth.simplify
+    else:
+        simple_polygons = polygons
+
     broadcast_message = BroadcastMessage(
         service_id=authenticated_service.id,
         content=broadcast_json['content'],
@@ -59,7 +64,7 @@ def create_broadcast():
             'names': [
                 area['name'] for area in broadcast_json['areas']
             ],
-            'simple_polygons': polygons.smooth.simplify.as_coordinate_pairs_lat_long,
+            'simple_polygons': simple_polygons.as_coordinate_pairs_lat_long,
         },
         status=BroadcastStatusType.PENDING_APPROVAL,
         api_key_id=api_user.id,