Requests to restore, resize, and reposition Browser windows will be
coming from the WebContent process rather than the WebDriver process.
Add hooks to propagate these requests back up to the Browser.
The spec notes "The specification does not guarantee that the resulting
window size will exactly match that which was requested", so these new
methods return the actual new size/position.
This patch adds WebView::ViewImplementation with all the
`notify_server_did_this_or_that()` functions from OOPWV.
This will allow us to share code between different web views, paving the
way for a Qt widget in Ladybird that can talk to a WebContent process.
