<!--  As an open source project with a dedicated but small maintainer team, it can sometimes take a long time for issues to be addressed so please be patient and we will get back to you as soon as we can.
-->

### Preflight Checklist
<!-- Please ensure you've completed the following steps by replacing [ ] with [x]-->

* [x] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
* [x] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
* [x] I have searched the issue tracker for a feature request that matches the one I want to file, without success.

### Problem Description
<!-- Is your feature request related to a problem? Please add a clear and concise description of what the problem is. -->
The `BrowserView` is much like `BrowserWindow`, but it cannot be used as a "window" for the `new-window` event.

Imagine a tabbed layout with several `BrowserView`s, much like the regular browser window. The `webPreferences.nativeWindowOpen` is enabled.

*Use-case 1:* The page inside one `BrowserView` tries to open a new window via `window.open()`. There's no way to handle `new-window` and create a new `BrowserView` such that the `window.opener` JavaScript property refers to its opener.

*Use-case 2:* A `<form target="_blank" method="POST">` inside `BrowserView` is submitted. A new `BrowserView` can be created and its `WebContents` `loadURL()` method can be used to navigate using `POST` method. But AFAIK there's no way to know what exactly `postData` that form was going to POST.

It works fine if the `new-window` is default-prevented and a new `BrowserWindow` is created with the `options.webContents` as a constructor option. But it is ignored for a `BrowserView`

### Proposed Solution
<!-- Describe the solution you'd like in a clear and concise manner -->
- Allow setting `webContents` in a `BrowserView` constructor options.
- Allow `BrowserView` to be a `e.newGuest` in a default-prevented `new-window` event.

### Alternatives Considered
<!-- A clear and concise description of any alternative solutions or features you've considered. -->

### Additional Information
<!-- Add any other context about the problem here. -->

shell/browser/api/electron_api_web_contents.cc
gin::StringToV8(isolate, "Failed to serialize arguments")));
    return false;
  }
  int32_t frame_id;
  int32_t process_id;
  if (gin::ConvertFromV8(isolate, frame, &frame_id)) {
    process_id = ontents()->GetMainFrame()->GetProcess()->GetID();
  } else {
    std::vector<int32_t> id_pair;
    if (gin::ConvertFromV8(isolate, frame, &id_pair) && id_pair.size() == 2) {
      process_id = id_pair[0];
      frame_id = id_pair[1];
    } else {
      isolate->ThrowException(v8::Exception::Error(gin::StringToV8(
          isolate,
          "frameId must be a number or a pair of [processId, frameId]")));
      return false;
    }
  }
  auto* rfh = content::RenderFrameHost::FromID(process_id, frame_id);
  if (!rfh || !rfh->IsRenderFrameLive() ||
      content::WebContents::FromRenderFrameHost(rfh) != ontents())
    return false;
  mojo::AssociatedRemote<mojom::ElectronRenderer> electron_renderer;
  rfh->GetRemoteAssociatedInterfaces()->GetInterface(&electron_renderer);
  electron_renderer->Message(internal, channel, std::move(message),
                             0 /* sender_id */);
  return true;
}
void WebContents::SendInputEvent(v8::Isolate* isolate,