Support TS exactOptionalPropertyTypes (fixes #35280) (#35281)

fixes #35280

Before:

![image](https://user-images.githubusercontent.com/343837/158047041-d4b65f19-c090-496b-b0c1-75faa388ea66.png)

After:

![image](https://user-images.githubusercontent.com/343837/158046975-7393f818-be1a-4d03-99db-643e88595657.png)

Author: quisido

packages/next/server/base-server.ts

@@ -672,7 +672,7 @@ export default abstract class Server<ServerOptions extends Options = Options> {
     fsRoutes: Route[]
     redirects: Route[]
     catchAllRoute: Route
-    catchAllMiddleware?: Route
+    catchAllMiddleware?: Route | undefined
     pageChecker: PageChecker
     useFileSystemPublicRoutes: boolean
     dynamicRoutes: DynamicRoutes | undefined

packages/next/shared/lib/router/router.ts

@@ -459,10 +459,10 @@ export type BaseRouter = {
   query: ParsedUrlQuery
   asPath: string
   basePath: string
-  locale?: string
-  locales?: string[]
-  defaultLocale?: string
-  domainLocales?: DomainLocale[]
+  locale?: string | undefined
+  locales?: string[] | undefined
+  defaultLocale?: string | undefined
+  domainLocales?: DomainLocale[] | undefined
   isLocaleDomain: boolean
 }
 
@@ -637,11 +637,11 @@ export default class Router implements BaseRouter {
   events: MittEmitter<RouterEvent>
   _wrapApp: (App: AppComponent) => any
   isSsr: boolean
-  _inFlightRoute?: string
-  _shallow?: boolean
-  locales?: string[]
-  defaultLocale?: string
-  domainLocales?: DomainLocale[]
+  _inFlightRoute?: string | undefined
+  _shallow?: boolean | undefined
+  locales?: string[] | undefined
+  defaultLocale?: string | undefined
+  domainLocales?: DomainLocale[] | undefined
   isReady: boolean
   isLocaleDomain: boolean