LanguageServers/Cpp: Use FileDB and AutoCompleteEngine base class

Author: https://github.com/itamar8910
Commit: 02038a0ede
Pull-request: https://github.com/SerenityOS/serenity/pull/5244
Reviewed-by: https://github.com/alimpfard

Userland/DevTools/HackStudio/LanguageServers/Cpp/CMakeLists.txt

@@ -1,8 +1,10 @@
 set(SOURCES
+    AutoCompleteEngine.cpp
     ClientConnection.cpp
-    main.cpp
+    FileDB.cpp
     LexerAutoComplete.cpp
     ParserAutoComplete.cpp
+    main.cpp
 )
 
 set(GENERATED_SOURCES