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/CppLanguageClient.ipc

@@ -0,0 +1,4 @@
+endpoint CppLanguageClient = 8002
+{
+    Dummy() =|
+}