Function: sh-font-lock-open-heredoc

Determine the syntax of the \n after a < START is the position of <<.
STRING is the actual word used as delimiter (e.g. "EOF").
INDENTED is non-nil if the here document's content (and the EOF mark) can
be indented (i.e. a <<- was used rather than just <<).
Point is at the beginning of the next line.