Use a fixed image for one-way arrows, not from the basemap. #20

Doesn't really solve the problem yet, because switching basemaps erases
the extra images loaded in maplibre

web/src/App.svelte

@@ -1,4 +1,5 @@
 <script lang="ts">
+  import onewayArrowUrl from "../assets/arrow.png?url";
   import logo from "../assets/logo.svg?url";
   import "@picocss/pico/css/pico.jade.min.css";
   import initLtn from "backend";
@@ -110,6 +111,10 @@
           id: "school_street",
           url: `${import.meta.env.BASE_URL}/filters/school_street_icon.gif`,
         },
+        {
+          id: "oneway-arrow",
+          url: onewayArrowUrl,
+        },
       ]}
     >
       <Geocoder />

web/src/OneWayLayer.svelte

@@ -1,8 +1,6 @@
 <script lang="ts">
   import { layerId } from "./common";
   import { SymbolLayer } from "svelte-maplibre";
-
-  // TODO Using the icon from maptiler basemap, so it won't work on some basemaps
 </script>
 
 <SymbolLayer
@@ -13,7 +11,7 @@
     ["!=", ["get", "direction"], "both"],
   ]}
   layout={{
-    "icon-image": "oneway",
+    "icon-image": "oneway-arrow",
     "icon-size": 1.0,
     "symbol-placement": "line",
     "symbol-spacing": 50,