Unable to copy assets folder to dist in Electron Types, need help on package.json

I am fresher to Electron and TypeScript. I am able to run the simple electron app using Typescript.

Now I wanted to use Splash screen. When I manually copy the image to dist folder, the splash screen comes and all work fine. How can I build the application using yarn build command so that assets folder should be copied to dist folder. My lead said that the copy should work for all platform. I have tried with the following package.json file. It is not an Angular project. It is a simple project.

{
  "name": "electron-quick-start-typescript",
  "version": "1.0.0",
  "description": "A minimal Electron application written with Typescript",
  "scripts": {
    "copy": "npm run copy:assets",
    "copy:assets": "cp -r assets/* dist",
    "build1": "tsc -p tsconfig.json && npm run copy",
    "build": "tsc -p tsconfig.json",
    "build:watch": "tsc -p tsconfig.json --watch",
    "copy:assets1": "copy -R /assets dist/assets/",
    "copy-files": "xcopy ./assets/*.* ./dist/assets",
    "build11": "tsc",
    "watch": "tsc -w",
    "lint": "tslint -c tslint.json -p tsconfig.json",
    "start": "npm run build && electron ./dist/main.js"
  },
  "repository": "https://github.com/electron/electron-quick-start-typescript",
  "build": {
    "extraResources": [
      {
        "from": "./src/assets/",
        "to": "dist",
        "filter": [
          "**/*"
        ]
      }
    ]
  },
  "keywords": [
    "Electron",
    "quick",
    "start",
    "tutorial",
    "demo",
    "typescript"
  ],
  "author": "GitHub",
  "license": "CC0-1.0",
  "devDependencies": {
    "electron": "^9.0.4",
    "tslint": "^6.1.2",
    "typescript": "^3.9.5",
    "@trodi/electron-splashscreen": "1.0.0",
    "babel-cli": "^6.11.4",
    "babel-preset-es2015": "^6.9.0",
    "browser-sync": "^2.14.0"
  }
}