Fix some typescript issues (#32586)

Fixes around 30 or so typescript errors. No runtime changes.

web_src/js/modules/fetch.ts

@@ -9,7 +9,7 @@ const safeMethods = new Set(['GET', 'HEAD', 'OPTIONS', 'TRACE']);
 // fetch wrapper, use below method name functions and the `data` option to pass in data
 // which will automatically set an appropriate headers. For json content, only object
 // and array types are currently supported.
-export function request(url: string, {method = 'GET', data, headers = {}, ...other}: RequestOpts = {}) {
+export function request(url: string, {method = 'GET', data, headers = {}, ...other}: RequestOpts = {}): Promise<Response> {
   let body: RequestData;
   let contentType: string;
   if (data instanceof FormData || data instanceof URLSearchParams) {