Add poi-milestone icon, use on railway milestone, boundary stone presets

data/presets/presets.json

@@ -6489,7 +6489,7 @@
             "name": "Archaeological Site"
         },
         "historic/boundary_stone": {
-            "icon": "monument",
+            "icon": "poi-milestone",
             "fields": [
                 "inscription"
             ],
@@ -10400,7 +10400,7 @@
             "name": "Railway Crossing (Road)"
         },
         "railway/milestone": {
-            "icon": "triangle-stroked",
+            "icon": "poi-milestone",
             "geometry": [
                 "point",
                 "vertex"

data/presets/presets/historic/boundary_stone.json

@@ -1,5 +1,5 @@
 {
-    "icon": "monument",
+    "icon": "poi-milestone",
     "fields": [
         "inscription"
     ],

data/presets/presets/railway/milestone.json

@@ -1,5 +1,5 @@
 {
-    "icon": "triangle-stroked",
+    "icon": "poi-milestone",
     "geometry": [
         "point",
         "vertex"