Be more aggresive classifying Roundabout Intersections.

Roundabout Intersections are roundabouts with up to four ways and turn
angles which makes the turns obvious, e.g. as in:

```
    *
    *
* *   * *
    *
    *
```

but not

```
     *
    *
* *   *
    * *
     * *
```

For Roundabout Intersections we issue instructions such as
"turn <direction>" instead of "take the <nth> exit".

At the moment we have a limit on the radius for these Roundabout
Intersections of 5 meters. Which fails to classify a wide range of
Roundabout Intersections in the US (with the US-wide streets).

This changeset removes the Roundabout Intersection radius limit:

- if the roundabout is larger than a threshold and is named we classify
  it as a rotary

- if the roundabout matches our criteria for Roundabout Intersections
  we classify it as a Roundabout Intersection

- else fallback to plain old Roundabout

There is a second issue with determining a roundabout's radius.
But that's for another pull request (tracking in #2716).

References:
- https://github.com/Project-OSRM/osrm-backend/issues/2716

src/extractor/guidance/roundabout_handler.cpp

@@ -321,37 +321,26 @@ RoundaboutType RoundaboutHandler::getRoundaboutType(const NodeID nid) const
     if (std::isinf(radius))
         return RoundaboutType::Roundabout;
 
-    // not within the dedicated radii for special roundabouts
-    if (radius > MAX_ROUNDABOUT_INTERSECTION_RADIUS && radius <= MAX_ROUNDABOUT_RADIUS)
-        return RoundaboutType::Roundabout;
+    // Looks like a rotary: large roundabout with dedicated name
+    // do we have a dedicated name for the rotary, if not its a roundabout
+    // This function can theoretically fail if the roundabout name is partly
+    // used with a reference and without. This will be fixed automatically
+    // when we handle references separately or if the useage is more consistent
+    const auto is_rotary = 1 == roundabout_name_ids.size() &&                          //
+                           0 == connected_names.count(*roundabout_name_ids.begin()) && //
+                           radius > MAX_ROUNDABOUT_RADIUS;
 
-    if (radius > MAX_ROUNDABOUT_RADIUS)
-    {
-        // do we have a dedicated name for the rotary, if not its a roundabout
-        // This function can theoretically fail if the roundabout name is partly
-        // used with a reference and without. This will be fixed automatically
-        // when we handle references separately or if the useage is more consistent
+    if (is_rotary)
+        return RoundaboutType::Rotary;
 
-        if (1 == roundabout_name_ids.size() &&
-            0 == connected_names.count(*roundabout_name_ids.begin()))
-            return RoundaboutType::Rotary;
-        else
-            return RoundaboutType::Roundabout;
-    }
+    // Looks like an intersection: four ways and turn angles are easy to distinguish
+    const auto is_roundabout_intersection = qualifiesAsRoundaboutIntersection(roundabout_nodes) &&
+                                            radius < MAX_ROUNDABOUT_INTERSECTION_RADIUS;
 
-    if (radius <= MAX_ROUNDABOUT_INTERSECTION_RADIUS)
-    {
-        const bool qualifies_as_roundabout_intersection =
-            qualifiesAsRoundaboutIntersection(roundabout_nodes);
-        if (qualifies_as_roundabout_intersection)
-        {
-            return RoundaboutType::RoundaboutIntersection;
-        }
-        else
-        {
-            return RoundaboutType::Roundabout;
-        }
-    }
+    if (is_roundabout_intersection)
+        return RoundaboutType::RoundaboutIntersection;
+
+    // Not a special case, just a normal roundabout
     return RoundaboutType::Roundabout;
 }