Ladybird/WebDriver: Move to using local socket files for WebDriver IPC

This allows us to use standard Serenity IPC infrastructure rather than
manually creating FD-passing sockets. This also lets us use Serenity's
WebDriver Session class, removing the copy previously used in Ladybird.
This ensures any changes to Session in the future will be picked up by
Ladybird for free.

Ladybird/WebDriver/CMakeLists.txt

@@ -2,9 +2,9 @@ set(WEBDRIVER_SOURCE_DIR ${SERENITY_SOURCE_DIR}/Userland/Services/WebDriver)
 
 set(SOURCES
     ${WEBDRIVER_SOURCE_DIR}/Client.cpp
+    ${WEBDRIVER_SOURCE_DIR}/Session.cpp
     ${WEBDRIVER_SOURCE_DIR}/WebContentConnection.cpp
     ../Utilities.cpp
-    Session.cpp
     main.cpp
 )