Investigate moving away from DO (Distributed Object) as IPC mechanism

MacVim currently uses Distributed Object as a way to communicate between individual Vim processes and MacVim but it's long been deprecated by Apple. See https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/DistrObjects/DistrObjects.html. As such, all usages of NSConnection are currently throwing deprecation warning.

Instead, Apple's preferred APIs are the XPC system: https://developer.apple.com/documentation/xpc

We should investigate whether to move off DO to either Apple's XPC or another IPC mechanism (for example, Neovim has its own IPC mechanism via msgpack). Since the DO implementation is the underlying system that we talks between MacVim GUI and Vim process, and there are a few quirks and back-and-forth messaging, we should make sure it keeps working (some edge cases includes window resizing with/without guioption-k, fullscreen, input, etc), and latency won't be affected as a result.

Also, occasionally we see error messages with DO (#1005), and I have seen issues with running unit tests locally if I have certain settings that seem to stem from DO init race connection, so hopefully we can eliminate those as well.

Beginne damit, die bestehende Verwendung von NSConnection und Distributed Object zwischen der MacVim GUI und dem Vim-Prozess zu lokalisieren. Lies die XPC-Dokumentation von Apple und vergleiche sie mit dem im Issue erwähnten alternativen IPC-Ansatz. Als abgeschlossen gilt die Identifizierung eines praktikablen Ersatzes sowie die Validierung von Kommunikation, Fenstergrößenänderung, Vollbildmodus, Eingabe, Latenz und den gemeldeten Verbindungsfehlern und Test-Race-Conditions.