src/common/util.js/isPreviousLineEmpty
function isPreviousLineEmpty(text, node, locStart) {
  let idx = locStart(node) - 1;
  idx = skipSpaces(text, idx, { backwards: true });
  idx = skipNewline(text, idx, { backwards: true });
  idx = skipSpaces(text, idx, { backwards: true });
  const idx2 = skipNewline(text, idx, { backwards: true });
  return idx !== idx2;
}