### Preflight Checklist

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

### Electron Version

14.2.0 / 15.3.0 / 16.0.0-beta.6

### What operating system are you using?

macOS

### Operating System Version

macOS Catalina 10.15.7

### What arch are you using?

x64

### Last Known Working Electron version

14.0.0 / 15.0.0-beta.2

### Expected Behavior

`<webview>` element should support trasparency. Check the included Fiddle sample.

### Actual Behavior

`<webview>` element transparency is broken

### Testcase Gist URL

_No response_

### Additional Information
[webview-transparency.zip](https://github.com/electron/electron/files/7464785/webview-transparency.zip)

<img width="912" alt="Screen Shot 2021-11-03 at 1 55 47 AM" src="https://user-images.githubusercontent.com/1281234/139971477-2077f353-c17c-417f-9f13-9c5c52139efa.png">
<img width="912" alt="Screen Shot 2021-11-03 at 1 55 53 AM" src="https://user-images.githubusercontent.com/1281234/139971481-49f8afa5-3024-46ba-9339-33c492ba3677.png">

Related to:
https://github.com/electron/electron/blob/2a2a1a834c7072226e9368f36fe0d22a125803f0/shell/browser/api/electron_api_web_contents.cc#L1461

It regressed in this ranges:
- https://github.com/electron/electron/compare/v14.0.0...v14.0.1 (probably #30819)
- https://github.com/electron/electron/compare/v15.0.0-beta.2...v15.0.0-beta.3 (probably #30777)
shell/browser/api/electron_api_web_contents.cc
}
#if !defined(OS_MAC)
   If the view's renderer is suspended this may fail on Windows/Linux -
   bail if so. See CopyFromSurface in
   content/public/browser/render_widget_host_view.h.
  auto* rfh = ontents()->GetMainFrame();
  if (rfh &&
      rfh->GetVisibilityState() == blink::mojom::PageVisibilityState::kHidden) {
    promise.Resolve(gfx::Image());
    return handle;
  }
#endif   defined(OS_MAC)
   Capture full page if user doesn't specify a |rect|.
  const gfx::Size view_size =
      rect.IsEmpty() ? view->GetViewBounds().size() : rect.size();
   By default, the requested bitmap size is the view size in screen
   coordinates.  However, if there's more pixel detail available on the
   current system, increase the requested bitmap size to capture it all.
  gfx::Size bitmap_size = view_size;
  const gfx::NativeView native_view = view->GetNativeView();
  const float scale = display::Screen::GetScreen()
                          ->GetDisplayNearestView(native_view)
                          .device_scale_factor();
  if (scale > 1.0f)
    bitmap_size = gfx::ScaleToCeiledSize(view_size, scale);
  view->CopyFromSurface(gfx::Rect(rect.origin(), view_size), bitmap_size,
                        base::BindOnce(&OnCapturePageDone, std::move(promise)));
  return handle;
}
void WebContents::IncrementCapturerCount(gin::Arguments* args) {