search: switch to new tag search parser in a few places.

app/logical/post_query.rb

@@ -4,7 +4,7 @@ class PostQuery
   extend Memoist
 
   attr_reader :search, :parser, :ast
-  delegate :tag_names, to: :ast
+  delegate :tag_names, :metatags, to: :ast
 
   def initialize(search)
     @search = search
@@ -16,5 +16,21 @@ class PostQuery
     Tag.where(name: tag_names)
   end
 
+  def is_single_tag?
+    ast.tag?
+  end
+
+  def select_metatags(*names)
+    metatags.select { |metatag| metatag.name.in?(names.map(&:to_s).map(&:downcase)) }
+  end
+
+  def has_metatag?(*names)
+    select_metatags(*names).present?
+  end
+
+  def find_metatag(*names)
+    select_metatags(*names).first&.value
+  end
+
   memoize :tags
 end