HackStudio: Add C++ Language Server

The language server keeps track of the content of currently edited
files by receiving updates about edit actions.

Also, C++ autocompletion is no longer tied to HackStudio itself and
moved to be part of the language server.

DevTools/HackStudio/LanguageServers/Cpp/CMakeLists.txt

@@ -0,0 +1,16 @@
+compile_ipc(CppLanguageServer.ipc CppLanguageServerEndpoint.h)
+compile_ipc(CppLanguageClient.ipc CppLanguageClientEndpoint.h)
+
+set(SOURCES
+    ClientConnection.cpp
+    main.cpp
+    CppLanguageServerEndpoint.h
+    CppLanguageClientEndpoint.h
+    AutoComplete.cpp
+)
+
+serenity_bin(CppLanguageServer)
+
+# We link with LibGUI because we use GUI::TextDocument to update 
+# the content of files according to the edit actions we receive over IPC.
+target_link_libraries(CppLanguageServer LibIPC LibCpp LibGUI)