Add GET /api/v2/search which returns rich tag objects, adjust web UI (#7661)

app/serializers/rest/v2/search_serializer.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class REST::V2::SearchSerializer < ActiveModel::Serializer
+  has_many :accounts, serializer: REST::AccountSerializer
+  has_many :statuses, serializer: REST::StatusSerializer
+  has_many :hashtags, serializer: REST::TagSerializer
+end