Limit parsing of endless heredocs

[nobodywasishere]

It would be useful if possible, when a heredoc_end isn't found, that the rest of the file isn't captured by the heredoc_content, and instead terminates early on the following line (where the heredoc_body starts)

So that example would be something like:

(source_file
  (call
    receiver: (identifier)
    method: (identifier)
    arguments: (argument_list
      (heredoc_start)
      (identifier))
 (heredoc_body
   (heredoc_content) # this would be empty or not part of the tree
   (MISSING 'HEREDOC_END')) # this would be on the line following the heredoc_start
 (call
   method: (identifier)
   arguments: (argument_list
     (string)))