Custom downloads

It would be great to have some kind of API to manually trigger a download of a given URL, for example to download adblocking lists when implementing an adblocker.

Another use case would be to allow an user to download a link via other means than a context menu.

void WebContentsAdapter::download(const QUrl &url, const QString &suggestedFileName) already exists, so I think all it'd take is to make that some kind of public API, instead of only allowing it to be used via QWebEnginePage::triggerAction and context menu data.