Add turning_circle field (#562)

* Add `turning_circle` field

* rename field label to "Shape"

Co-authored-by: Martin Raifer <martin@raifer.tech>

data/fields/turning_circle.json

@@ -0,0 +1,5 @@
+{
+    "key": "turning_circle",
+    "type": "combo",
+    "label": "Shape"
+}

data/presets/highway/turning_circle.json

@@ -3,6 +3,9 @@
     "geometry": [
         "vertex"
     ],
+    "fields": [
+        "turning_circle"
+    ],
     "tags": {
         "highway": "turning_circle"
     },