Fix multiline paragraph rendering as single line (#7210)

src/Markdown.ts

@@ -56,6 +56,12 @@ function isAllowedHtmlTag(node: commonmark.Node): boolean {
 function isMultiLine(node: commonmark.Node): boolean {
  let par = node;
  while (par.parent) {
+ // commonmark Parser separate quotes with blank quoted lines between them with
+ // paragraphs, so we need to consider it when the markdown is only a multiline quote.
+ if (par.type === 'block_quote') {
+ break;
+ }
+
  par = par.parent;
  }
  return par.firstChild != par.lastChild;