Add ability to follow hashtags (#18809)

app/presenters/tag_relationships_presenter.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+class TagRelationshipsPresenter
+  attr_reader :following_map
+
+  def initialize(tags, current_account_id = nil, **options)
+    @following_map = begin
+      if current_account_id.nil?
+        {}
+      else
+        TagFollow.select(:tag_id).where(tag_id: tags.map(&:id), account_id: current_account_id).each_with_object({}) { |f, h| h[f.tag_id] = true }.merge(options[:following_map] || {})
+      end
+    end
+  end
+end