Improve waterbox startup with compilation changes

Prerequisite: Switch to .NET Core.

Waterbox executables need to be loaded to a predictable address. It's too hard to guarantee this address in the first 2G for space, so we put it out in the hood, typically 0x36f00000000. This means code is compiled with -mcmodel=large, which hurts perf.

.NET core gives us opportunities to fix this.

https://github.com/dotnet/samples/tree/master/core/hosting

We would make a small unmanaged executable that:

1. ran a few intitial startup checks (some of the stuff that zeromuisan tries to do now can get foiled when assemblies accidentally load too early)
2. blocked off some address space for waterbox
3. booted a CLR instance and loaded the main emuhawk assembly

edit: Maybe https://github.com/SnowflakePowered/sabinokaku can do this? --yoshi

TODO.

Start with the linked .NET Core hosting samples and verify the prerequisite of switching to .NET Core. Then map how Waterbox executables are currently started and compiled, including the startup checks and address-space reservation described here. Done should be a decided and implemented startup design that avoids the current large code model, with its effects validated.