chore: extend linting of code blocks in the docs (#40245)

* chore: extend linting of code blocks in the docs

* chore: combine lint:markdownlint and lint:markdown scripts

docs/api/screen.md

@@ -14,20 +14,29 @@ property, so writing `let { screen } = require('electron')` will not work.
 
 An example of creating a window that fills the whole screen:
 
-```javascript fiddle='docs/fiddles/screen/fit-screen'
-const { app, BrowserWindow, screen } = require('electron')
+```fiddle docs/fiddles/screen/fit-screen
+// Retrieve information about screen size, displays, cursor position, etc.
+//
+// For more info, see:
+// https://www.electronjs.org/docs/latest/api/screen
+
+const { app, BrowserWindow, screen } = require('electron/main')
+
+let mainWindow = null
 
-let win
 app.whenReady().then(() => {
-  const { width, height } = screen.getPrimaryDisplay().workAreaSize
-  win = new BrowserWindow({ width, height })
-  win.loadURL('https://github.com')
+  // Create a window that fills the screen's available work area.
+  const primaryDisplay = screen.getPrimaryDisplay()
+  const { width, height } = primaryDisplay.workAreaSize
+
+  mainWindow = new BrowserWindow({ width, height })
+  mainWindow.loadURL('https://electronjs.org')
 })
 ```
 
 Another example of creating a window in the external display:
 
-```javascript
+```js
 const { app, BrowserWindow, screen } = require('electron')
 
 let win