Refactor JSON templates to be generated with ActiveModelSerializers instead of Rabl (#4090)

app/serializers/rest/relationship_serializer.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+class REST::RelationshipSerializer < ActiveModel::Serializer
+  attributes :id, :following, :followed_by, :blocking,
+             :muting, :requested, :domain_blocking
+
+  def following
+    instance_options[:relationships].following[object.id] || false
+  end
+
+  def followed_by
+    instance_options[:relationships].followed_by[object.id] || false
+  end
+
+  def blocking
+    instance_options[:relationships].blocking[object.id] || false
+  end
+
+  def muting
+    instance_options[:relationships].muting[object.id] || false
+  end
+
+  def requested
+    instance_options[:relationships].requested[object.id] || false
+  end
+
+  def domain_blocking
+    instance_options[:relationships].domain_blocking[object.id] || false
+  end
+end