Handle case when heredoc closing identifier is indented with space or tabulation
requested to merge alainl/syntax-highlighting:add-support-of-indented-heredoc-closing-identifier into master
That syntax is allowed since PHP 7.3.0 => https://www.php.net/manual/en/language.types.string.php#language.types.string.syntax.heredoc
Edited by Alain Laporte