Browser: Add a basic WebDriver API

This adds a new option "--webdriver" that opens a local unix socket
in /tmp/browser_{pid} which the WebDriver server can use to send
commands to the Browser instance.

Co-authored-by: Florent Castelli <florent.castelli@gmail.com>

Userland/Applications/Browser/WebDriverSessionClient.ipc

@@ -0,0 +1,9 @@
+#include <AK/URL.h>
+
+endpoint WebDriverSessionClient {
+    quit() =|
+
+    get_url() => (URL url)
+    set_url(URL url) =|
+    get_title() => (String title)
+}