feat: ready-to-show event on webContents

[KanishkRanjan]

Description of Change

Fixes #43531

Feat: add paintWhenInitiallyHidden option to WebContentsView

This PR adds a paintWhenInitiallyHidden option to the WebContentsView constructor.

Setting this flag to true ( which is default ) "wakes up" the renderer so it can fire ready-to-show and correctly set its initial visibilityState to hidden while still in the background.

⚠️ This PR introduces a breaking change ⚠️.

Checklist

• PR description included
• npm test passes
• tests are changed or added
• relevant API documentation, tutorials, and examples are updated and follow the documentation style guide
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Added the paintWhenInitiallyHidden option to the WebContentsView constructor to allow background painting and initialization.

[welcome]

💖 Thanks for opening this pull request! 💖

Semantic PR titles

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

Commit signing

This repo enforces commit signatures for all incoming PRs.
To sign your commits, see GitHub's documentation on Telling Git about your signing key.

PR tips

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.

[nikwen]

Thanks for working on this!

I'll let someone else look at the C++ code who is more familiar with it.

[nikwen]

Two separate tests should be two separate it() calls.