Change public accounts pages to mount the web UI (#19319)

* Change public accounts pages to mount the web UI

* Fix handling of remote usernames in routes

- When logged in, serve web app
- When logged out, redirect to permalink
- Fix `app-body` class not being set sometimes due to name conflict

* Fix missing `multiColumn` prop

* Fix failing test

* Use `discoverable` attribute to control indexing directives

* Fix `<ColumnLoading />` not using `multiColumn`

* Add `noindex` to accounts in REST API

* Change noindex directive to not be rendered by default before a route is mounted

* Add loading indicator for detailed status in web UI

* Fix missing indicator appearing while account is loading in web UI

app/views/following_accounts/index.html.haml

@@ -1,20 +1,6 @@
-- content_for :page_title do
-  = t('accounts.people_followed_by', name: display_name(@account))
-
 - content_for :header_tags do
   %meta{ name: 'robots', content: 'noindex' }/
+
   = render 'accounts/og', account: @account, url: account_followers_url(@account, only_path: false)
 
-= render 'accounts/header', account: @account
-
-- if @account.hide_collections?
-  .nothing-here= t('accounts.network_hidden')
-- elsif user_signed_in? && @account.blocking?(current_account)
-  .nothing-here= t('accounts.unavailable')
-- elsif @follows.empty?
-  = nothing_here
-- else
-  .card-grid
-    = render partial: 'application/card', collection: @follows.map(&:target_account), as: :account
-
-  = paginate @follows
+= render 'shared/web_app'