LibWeb+WebContent: Add new console-message IPC calls

This patch introduces three new IPC calls for WebContent:

- `Client::did_output_js_console_message(index)`:
  Notifies the client that a new console message was logged.

- `Server::js_console_request_messages(start_index)`:
  Ask the server for console messages starting at the given index.

- `Client::did_get_js_console_messages(start_index, types, messages)`:
  Send the client the messages they requested.

This mechanism will replace the current
`Client::did_js_console_output()` call in the next few commits. This
will allow us to display messages in the console that happened before
the console was opened.

Userland/Services/WebContent/ClientConnection.cpp

@@ -283,6 +283,18 @@ void ClientConnection::js_console_initialize()
     }
 }
 
+void ClientConnection::initialize_js_console(Badge<PageHost>)
+{
+    auto* document = page().top_level_browsing_context().document();
+    auto interpreter = document->interpreter().make_weak_ptr();
+    if (m_interpreter.ptr() == interpreter.ptr())
+        return;
+
+    m_interpreter = interpreter;
+    m_console_client = make<WebContentConsoleClient>(interpreter->global_object().console(), interpreter, *this);
+    interpreter->global_object().console().set_client(*m_console_client.ptr());
+}
+
 void ClientConnection::js_console_input(const String& js_source)
 {
     if (m_console_client)
@@ -306,6 +318,11 @@ void ClientConnection::run_javascript(String const& js_source)
     }
 }
 
+void ClientConnection::js_console_request_messages(i32)
+{
+    TODO();
+}
+
 Messages::WebContentServer::GetSelectedTextResponse ClientConnection::get_selected_text()
 {
     return page().focused_context().selected_text();