[Statsig] Typecheck gates (#3467)

* Typecheck gates

* Lint against untyped useGate()

* Alphabetic

src/lib/statsig/gates.ts

@@ -1,3 +1,8 @@
-import {useGate} from './statsig'
-
-export const useNewSearchGate = () => useGate('new_search')
+export type Gate =
+  // Keep this alphabetic please.
+  | 'autoexpand_suggestions_on_profile_follow'
+  | 'disable_min_shell_on_foregrounding'
+  | 'disable_poll_on_discover'
+  | 'new_search'
+  | 'show_follow_back_label'
+  | 'start_session_with_following'

src/lib/statsig/statsig.tsx

@@ -11,6 +11,7 @@ import {
 import {logger} from '#/logger'
 import {useSession} from '../../state/session'
 import {LogEvents} from './events'
+import {Gate} from './gates'
 
 export type {LogEvents}
 
@@ -69,7 +70,7 @@ export function logEvent<E extends keyof LogEvents>(
   }
 }
 
-export function useGate(gateName: string) {
+export function useGate(gateName: Gate): boolean {
   const {isLoading, value} = useStatsigGate(gateName)
   if (isLoading) {
     // This should not happen because of waitForInitialization={true}.