Make it faster in the UI to flip between test cases. Useful for check…

…ing diffs in many places

web/src/common/import/Osm2streetsSettings.svelte

@@ -1,6 +1,4 @@
 <script lang="ts">
-  import LanePopup from "../../street-explorer/LanePopup.svelte";
-
   export let settings = {
     debug_each_step: false,
     dual_carriageway_experiment: false,

web/src/common/osm_input/BuiltInSelector.svelte

@@ -63,13 +63,33 @@
     testCase = prev;
     await reload();
   }
+
+  async function prev() {
+    let idx = list.indexOf(testCase);
+    if (idx != -1 && idx != 0) {
+      testCase = list[idx - 1];
+      await reload();
+    }
+  }
+
+  async function next() {
+    let idx = list.indexOf(testCase);
+    if (idx != -1 && idx != list.length - 1) {
+      testCase = list[idx + 1];
+      await reload();
+    }
+  }
 </script>
 
+<button on:click={prev} disabled={testCase == "none"}>&larr;</button>
+
 <select bind:value={testCase} on:change={reload}>
   <option value="none">None</option>
   {#each list as x}
     <option value={x}>{x}</option>
   {/each}
 </select>
 
+<button on:click={next} disabled={testCase == "none"}>&rarr;</button>
+
 <svelte:window on:popstate={popState} />