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/layouts/public.html.haml

@@ -1,60 +0,0 @@
-- content_for :header_tags do
-  = render_initial_state
-  = javascript_pack_tag 'public', crossorigin: 'anonymous'
-
-- content_for :content do
-  .public-layout
-    - unless @hide_navbar
-      .container
-        %nav.header
-          .nav-left
-            = link_to root_url, class: 'brand' do
-              = logo_as_symbol(:wordmark)
-
-            - unless whitelist_mode?
-              = link_to t('about.about_this'), about_more_path, class: 'nav-link optional'
-              = link_to t('about.apps'), 'https://joinmastodon.org/apps', class: 'nav-link optional'
-
-          .nav-center
-
-          .nav-right
-            - if user_signed_in?
-              = link_to t('settings.back'), root_url, class: 'nav-link nav-button webapp-btn'
-            - else
-              = link_to_login t('auth.login'), class: 'webapp-btn nav-link nav-button'
-              = link_to t('auth.register'), available_sign_up_path, class: 'webapp-btn nav-link nav-button'
-
-    .container= yield
-
-    .container
-      .footer
-        .grid
-          .column-0
-            %h4= t 'footer.resources'
-            %ul
-              %li= link_to t('about.privacy_policy'), privacy_policy_path
-          .column-1
-            %h4= t 'footer.developers'
-            %ul
-              %li= link_to t('about.documentation'), 'https://docs.joinmastodon.org/'
-              %li= link_to t('about.api'), 'https://docs.joinmastodon.org/client/intro/'
-          .column-2
-            %h4= link_to t('about.what_is_mastodon'), 'https://joinmastodon.org/'
-            = link_to logo_as_symbol, root_url, class: 'brand'
-          .column-3
-            %h4= site_hostname
-            %ul
-              - unless whitelist_mode?
-                %li= link_to t('about.about_this'), about_more_path
-              %li= "v#{Mastodon::Version.to_s}"
-          .column-4
-            %h4= t 'footer.more'
-            %ul
-              %li= link_to t('about.source_code'), Mastodon::Version.source_url
-              %li= link_to t('about.apps'), 'https://joinmastodon.org/apps'
-        .legal-xs
-          = link_to "v#{Mastodon::Version.to_s}", Mastodon::Version.source_url
-          ·
-          = link_to t('about.privacy_policy'), privacy_policy_path
-
-= render template: 'layouts/application'