LibCore: Add utility class for temporary files and directories

Core::TempFile is a RAII type that creates a temporary file or directory
on construction and deletes it on destruction.

Userland/Libraries/LibCore/CMakeLists.txt

@@ -33,6 +33,7 @@ set(SOURCES
     System.cpp
     TCPServer.cpp
     TCPSocket.cpp
+    TempFile.cpp
     Timer.cpp
     UDPServer.cpp
     UDPSocket.cpp