fix(forms-api): resolve type errors

Adds JSDoc annotations and corrects type casting to resolve TypeScript errors in the forms-api directory.

- Adds @param and @return annotations to functions.
- Casts the `method` property in `UrlFetchApp.fetch` options to the correct type.
- Removes unhelpful try/catch blocks.
- Fixes syntax errors in `retrieve_all_responses.gs`.
- Uses `response.getContentText()` instead of string coercion.

Author: google-labs-jules[bot]

forms-api/demos/AppsScriptFormsAPIWebApp/Code.gs

@@ -2,6 +2,7 @@
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
+// You may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     https://www.apache.org/licenses/LICENSE-2.0
@@ -12,6 +13,9 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+/**
+ * @return {GoogleAppsScript.HTML.HtmlOutput}
+ */
 function doGet() {
   return HtmlService.createTemplateFromFile('Main').evaluate();
-}
+}