Updates the types of proposed API relying on DOM (#16390)

* Updates the types of proposed API relying on DOM

* oops

src/api.proposed.jupyterSettings.d.ts

@@ -12,11 +12,18 @@ declare module './api' {
     export interface JupyterServerConnectionInformation {
         /**
          * The `fetch` method to use.
+         * The types of the parameters are not defined so as to avoid enforcing the use of `DOM` in `tsconfig.json`.
+         * The signature of this method matches the `fetch` method in the browser.
+         * https://developer.mozilla.org/en-US/docs/Web/API/Window/fetch
+         * fetch(input: RequestInfo, init?: RequestInit) =>Promise<Response>;
          */
-        readonly fetch?: (input: RequestInfo, init?: RequestInit) => Promise<Response>;
+        readonly fetch?: (input: any, init?: any) => Promise<any>;
         /**
          * The `WebSocket` object constructor.
+         * This matches the `WebSocket` object in the browser.
+         * https://developer.mozilla.org/en-US/docs/Web/API/WebSocket
+         * `typeof WebSocket`, made `any` so that `DOM` is not required in tsconfig for those not using this.
          */
-        readonly WebSocket?: typeof WebSocket;
+        readonly WebSocket?: any;
     }
 }