HackStudio: Abstract away language-server details

This commit moves all the logic that deals with the language server
(from HackStudio) into a LanguageClient class, provides some functions
to make constructing them easier, and makes all language servers use a
singular IPC definition.
Also fixes the FIXME about making the autocompletion async.
This makes adding language servers in the future significantly less
duplicate-y, and significantly easier :^)

DevTools/HackStudio/CMakeLists.txt

@@ -23,6 +23,7 @@ set(SOURCES
     Git/GitRepo.cpp
     Git/GitWidget.cpp
     HackStudioWidget.cpp
+    LanguageClient.cpp
     Locator.cpp
     ProcessStateWidget.cpp
     Project.cpp