message: feat(scroll): allow modifying scrollBehavior in options
  this allows enhanceApp in vuepress to run after creating the router
diff: @@ -333,7 +333,6 @@ export function createRouter(options: RouterOptions): Router {
  const matcher = createRouterMatcher(options.routes, options)
  let parseQuery = options.parseQuery || originalParseQuery
  let stringifyQuery = options.stringifyQuery || originalStringifyQuery
  - let { scrollBehavior } = options
  let routerHistory = options.history
  const beforeGuards = useCallbacks<NavigationGuardWithThis<undefined>>()
  @@ -345,7 +344,7 @@ export function createRouter(options: RouterOptions): Router {
  let pendingLocation: RouteLocation = START_LOCATION_NORMALIZED
  // leave the scrollRestoration if no scrollBehavior is provided
  - if (isBrowser && scrollBehavior && 'scrollRestoration' in history) {
  + if (isBrowser && options.scrollBehavior && 'scrollRestoration' in history) {
  history.scrollRestoration = 'manual'
  }
  @@ -1016,6 +1015,7 @@ export function createRouter(options: RouterOptions): Router {
  isPush: boolean,
  isFirstNavigation: boolean
  ): Promise<any> {
  + const { scrollBehavior } = options
  if (!isBrowser || !scrollBehavior) return Promise.resolve()
  let scrollPosition: _ScrollPositionNormalized | null =
  