Upgrade to .NET 5

[ekolis]

Describe the feature you'd like to see
Upgrade this game from .NET Framework 4.x or whatever it's running under now to .NET 5.

Benefits
Not much benefit for players, might improve performance slightly if we're lucky, but it would mean we can use all the cool new C# 9 features like record types, nullable reference types, enhanced pattern matching, and so on.

Describe alternatives
It's .NET 5, not really many alternatives there besides maybe switching to .NET Core 3.1, but that's entirely supplanted by .NET 5 anyway. Mono or Unity, perhaps?

Additional context
One potential problem is, if I'm not mistaken WinForms apps targeting .NET 5 will not run in Mono, so we could be losing Linux/Mac compatibility until someone fixes that or a future version of .NET makes WinForms cross-platform.

[ekolis]

I made some progress on this, but for some reason when I try to start a new game, the serializer crashes complaining that the mineral packet hull's "AllocatedComponent", whatever that is, is null...