LibDevTools+LibWebView: Support DevTools page reloads

Firefox reloads remote targets through the tab descriptor's
reloadDescriptor request. We advertised support for that request, but
left it unhandled, so Firefox could clear inspector state without
causing Ladybird to reload the page.

Route reloadDescriptor, and the legacy frame target reload request,
through the DevTools delegate to WebView's reload path. This lets the
existing navigation notifications publish the replacement inspector root
after the reload completes.