Use async functions in .svelte files (#1693)

* Use async functions in CodeMirror.svelte

* Fix using async functions by modifying svelte-preprocess output

* Revert "Fix using async functions by modifying svelte-preprocess output"

This reverts commit 94c9cadaaa.

Trying a different fix.

* Change TypeScript target to ES2019

ts/editor/CodeMirror.svelte

@@ -40,11 +40,12 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
     /**
      * Convenience function for editor.setOption.
      */
-    function setOption<T extends keyof CodeMirrorLib.EditorConfiguration>(
+    async function setOption<T extends keyof CodeMirrorLib.EditorConfiguration>(
         key: T,
         value: CodeMirrorLib.EditorConfiguration[T],
-    ): void {
+    ): Promise<void> {
-        editorPromise.then((editor) => editor.setOption(key, value));
+        const editor = await editorPromise;
+        editor.setOption(key, value);
     }
 
     const direction = getContext<Writable<"ltr" | "rtl">>(directionKey);
@@ -62,14 +63,13 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
     const dispatch = createEventDispatcher();
 
-    onMount(() =>
+    onMount(async () => {
-        editorPromise.then((editor) => {
+        const editor = await editorPromise;
         setupCodeMirror(editor, code);
         editor.on("change", () => dispatch("change", editor.getValue()));
         editor.on("focus", () => dispatch("focus"));
         editor.on("blur", () => dispatch("blur"));
-        }),
+    });
-    );
 </script>
 
 <div class="code-mirror">

ts/tsconfig.json

@@ -17,7 +17,7 @@
     "compilerOptions": {
         "declaration": true,
         "composite": true,
-        "target": "es6",
+        "target": "es2019",
         "module": "es2020",
         "lib": [
             "es2017",