Add web polyfills

src/state/lib/bg-scheduler.web.ts

@@ -0,0 +1,13 @@
+type BackgroundFetchStatus = 0 | 1 | 2
+
+export async function configure(
+  _handler: (taskId: string) => Promise<void>,
+  _timeoutHandler: (taskId: string) => Promise<void>,
+): Promise<BackgroundFetchStatus> {
+  // TODO
+  return 0
+}
+
+export function finish(_taskId: string) {
+  // TODO
+}