GROUP_HEREDOC_LINE_BODY tests

Add tests for all (non-bad) characters handled by
GROUP_HEREDOC_LINE_BODY.  These tests caught a bug where
GROUP_HEREDOC_LINE_START, which is prior state for
GROUP_HEREDOC_LINE_BODY, did not handle EOL, which means completely
blank lines (with no spaces) could not be handled in
GROUP_HEREDOC_LINE_START.