Add style loading indicator, fix #1626

src/UI/Map/StyleLoadingIndicator.svelte

@@ -0,0 +1,19 @@
+<script lang="ts">
+  import Loading from "../Base/Loading.svelte"
+  import { Stores, UIEventSource } from "../../Logic/UIEventSource"
+  import { Map as MlMap } from "maplibre-gl"
+  import { onDestroy } from "svelte"
+
+  let isLoading = false
+  export let map: UIEventSource<MlMap>
+  onDestroy(Stores.Chronic(250).addCallback(
+    () => {
+      isLoading = !map.data?.isStyleLoaded()
+    },
+  ))
+</script>
+
+
+{#if isLoading}
+  <Loading />
+{/if}