message: Improve DeclarePairedDelimiter preview support
  Related to
diff: @@ -26,7 +26,7 @@ export class MathPreview {
  return commands.replace(/\\providecommand/g, '\\newcommand')
  .replace(/\\newcommand\*/g, '\\newcommand')
  .replace(/\\renewcommand\*/g, '\\renewcommand')
  - .replace(/\\DeclarePairedDelimiter{(\\[a-zA-Z]+)}{([^{}]*)}{([^{}]*)}/g, '\\newcommand{$1}[1]{\\left$2 #1 \\right$3}')
  + .replace(/\\DeclarePairedDelimiter{(\\[a-zA-Z]+)}{([^{}]*)}{([^{}]*)}/g, '\\newcommand{$1}[2][]{#1$2 #2 #1$3}')
  }
  private async loadNewCommandFromConfigFile(newCommandFile: string) {
  @@ -98,7 +98,7 @@ export class MathPreview {
  const name = latexParser.stringify(node.args[0])
  const leftDelim = latexParser.stringify(node.args[1]).slice(1, -1)
  const rightDelim = latexParser.stringify(node.args[2]).slice(1, -1)
  - const s = `\\newcommand${name}[1]{\\left${leftDelim} #1 \\right${rightDelim}}`
  + const s = `\\newcommand${name}[2][]{#1${leftDelim} #2 #1${rightDelim}}`
  commands.push(s)
  }
  }
  