Add optional support for bundling CEF

[YoavCodes]

By default Electrobun uses the system webview. This lets the OS manage security updates decoupled from your application and reduces bundle size.

Some users want the option to bundle a cross-platform renderer (like CEF or servo) because they prioritize quirks like CSS differences between renderers or require Chrome-based functionality like CDP in their applications over security and bundle size.

This task is to add the option for developers to bundle a cross-platform renderer