[netcore] System.Private.CoreLib changes to match runtime expectations. (#12504)
1. Add classes that the runtime depends on:
* System.Reflection.RuntimeAssembly and System.Reflection.MonoAssembly
* System.Mono.MonoDomain and System.Mono.MonoDomainSetup
2. Add fields to some classes so they match what `object-internals.h` expect on the native side.
3. Make a non-`abstract` `System.RuntimeType` stub.
`System.Type` and `System.RuntimeType` need to have fields that match `object-internals.h` and also the runtime wants to create instances of this type and things go wrong if it's abstract.
16 files changed: