Please error, or at least warn, when a managed type is included in INetworkSerializeByMemcpy

Is your feature request related to a problem? Please describe.

My coworker was unfamiliar with INetworkSerializeByMemcpy and the FixedStringNNNBytes types, and added a string field to an existing INetworkSerializeByMemcpy struct. This caused me great headaches (it made it into a publicly released patch), trying to track down segfault heap corruption that only showed up in very specific multiplayer circumstances (the string was normally null, which probably masked the issue).

Describe the solution you'd like

Please cause a build error when a managed type (a class, a string, or the like) is included in an INetworkSerializeByMemcpy type. I cannot think of any use case where it would be valid or intended to serialize a managed GC pointer by memcpy. At least a warning if nothing else.

It doesn't have to be perfect, even just checking for string would be lovely - string specifically is such a massive footgun, it's so easy to accidentally include and think it'll work fine. The fact it crashes later on via unrelated segfault heap corruption bringing down the editor, instead of a C# Exception, is especially rough.

Beginne damit, die Definition von INetworkSerializeByMemcpy sowie deren Validierungs- oder Serialisierungstests zu finden. Verfolge, wie implementierende Typen während der Kompilierung oder zur Laufzeit geprüft werden, und füge anschließend Abdeckung für String- und andere verwaltete Felder hinzu; als abgeschlossen gilt die Aufgabe, wenn solche Typen statt einer unsicheren memcpy-Serialisierung einen Build-Fehler oder eine Warnung erzeugen.