Build the tokenizer through the parse context for liquid-c (#1386)

lib/liquid/parse_context.rb

@@ -23,6 +23,10 @@ module Liquid
       Liquid::BlockBody.new
     end
 
+    def new_tokenizer(markup, start_line_number: nil, for_liquid_tag: false)
+      Tokenizer.new(markup, line_number: start_line_number, for_liquid_tag: for_liquid_tag)
+    end
+
     def parse_expression(markup)
       Expression.parse(markup)
     end