LibCore+LibIPC: Move SystemServerTakeover.{h,cpp} to LibCore

This functionality is required by Core::LocalServer and LibIPC depends
on LibCore.

take_over_accepted_socket_from_system_server has also been renamed to
take_over_socket_from_system_server as the socket need not be accepted
before taking it over. :^)

Userland/Libraries/LibCore/CMakeLists.txt

@@ -32,6 +32,7 @@ set(SOURCES
     Stream.cpp
     StandardPaths.cpp
     System.cpp
+    SystemServerTakeover.cpp
     TCPServer.cpp
     TCPSocket.cpp
     TempFile.cpp