docs: fix missing dependencies in ipc patterns

[chuion]

Fix missing dependencies in ipc patterns

• updated docs/fiddles/ipc/pattern-3/main.js otherwise it would have thrown "UnhandledPromiseRejectionWarning: ReferenceError: ipcMain is not defined"
• updated docs/fiddles/ipc/pattern-2/main.js to adapt coding style

There is a another bug in docs/fiddles/ipc/pattern-3/renderer.js : event.reply is undefined .

const counter = document.getElementById('counter')

window.electronAPI.handleCounter((event, value) => {
    const oldValue = Number(counter.innerText)
    const newValue = oldValue + value
    counter.innerText = newValue
    event.reply('counter-value', newValue)  // `event.reply` is undefined, `event.sender.send` is available.
})

Checklist

• relevant documentation is changed or added

Release Notes

Notes: none

[welcome]

💖 Thanks for opening this pull request! 💖

We use semantic commit messages to streamline the release process. Before your pull request can be merged, you should update your pull request title to start with a semantic prefix.

Examples of commit messages with semantic prefixes:

• fix: don't overwrite prevent_default if default wasn't prevented
• feat: add app.isPackaged() method
• docs: app.isDefaultProtocolClient is now available on Linux

Things that will help get your PR across the finish line:

• Follow the JavaScript, C++, and Python coding style.
• Run npm run lint locally to catch formatting errors earlier.
• Document any user-facing changes you've made following the documentation styleguide.
• Include tests when adding/changing behavior.
• Include screenshots and animated GIFs whenever possible.

We get a lot of pull requests on this repo, so please be patient and we will get back to you as soon as we can.

[jkleinsc]

Thanks for the PR @chuion!

[jkleinsc]

Merging as CI failure is unrelated and fixed in #33141.

[welcome]

Congrats on merging your first pull request! 🎉🎉🎉

[release-clerk]

No Release Notes