Improve blocked view of profiles (#10491)

* Revert "Fix filtering of favourited_by, reblogged_by, followers and following (#10447)"

This reverts commit 120544067f.

* Revert "Hide blocking accounts from blocked users (#10442)"

This reverts commit 62bafa20a1.

* Improve blocked view of profiles

- Change "You are blocked" to "Profile unavailable"
- Hide following/followers in API when blocked
- Disable follow button and show "Profile unavailable" on public profile as well

app/serializers/rest/relationship_serializer.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class REST::RelationshipSerializer < ActiveModel::Serializer
-  attributes :id, :following, :showing_reblogs, :followed_by, :blocking,
+  attributes :id, :following, :showing_reblogs, :followed_by, :blocking, :blocked_by,
              :muting, :muting_notifications, :requested, :domain_blocking,
              :endorsed
 
@@ -27,6 +27,10 @@ class REST::RelationshipSerializer < ActiveModel::Serializer
     instance_options[:relationships].blocking[object.id] || false
   end
 
+  def blocked_by
+    instance_options[:relationships].blocked_by[object.id] || false
+  end
+
   def muting
     instance_options[:relationships].muting[object.id] ? true : false
   end