message: add doc on a type-casting
diff: import * as vscode from 'vscode'
  import * as path from 'path'
  -import Jimp from 'jimp'
  -import * as JimpLib0 from 'jimp'
  import {Extension} from '../../main'
  import {PDFRenderer} from './pdfrenderer'
  import {svgToDataUrl} from '../../utils'
  +// workaround to avoid enabling esModuleInterop in tsconfig.json
  +// If esModuleInterop enabled, some other packages do not work.
  +import Jimp from 'jimp'
  +import * as JimpLib0 from 'jimp'
  const JimpLib = JimpLib0 as unknown as Jimp
  export class GraphicsPreview {
  