There are many things in Visual Studio that run out-of-process, and coordinate via IPC. It's an implementation detail, and does not change the fundamental approach.

Also, many things in VSCode can be done in-proc as well if one so desires, including debuggers and language servers. Most extensions do them out-of-proc because it gives them more flexibility (esp. wrt implementation language for those components), and because it's easier to test such isolated components.