Browser+LibWeb+WebContent: Allow Browser to load local files

To achieve this goal:
 - The Browser unveils "/tmp/portal/filesystemaccess"
 - Pass the page through LoadRequest => ResourceLoader
 - ResourceLoader requests a file to the FileSystemAccessServer via IPC
 - OutOfProcessWebView handles it and sends a file descriptor back to
 the Page.

Userland/Libraries/LibWebView/WebContentClient.cpp

@@ -200,4 +200,9 @@ void WebContentClient::did_update_resource_count(i32 count_waiting)
     m_view.notify_server_did_update_resource_count(count_waiting);
 }
 
+void WebContentClient::did_request_file(String const& path, i32 request_id)
+{
+    m_view.notify_server_did_request_file({}, path, request_id);
+}
+
 }