Tests: refactor TestFiles to easily test compilation against real mscorlib later.
Compiler: Rearrange order of how class and fields are initialized (avoid rare circular dependencies)
Compiler: string constants are now emitted with private linkage (avoid collision with other modules).
Compiler: use actual type of value when doing stack conversion.
Compiler: allow resolved method to be null while checking if it has PInvoke info.
Compiler: Factorized code that converts from integer or pointer to native-sized integer (used for newarr, ldelem, ldelema & stelem).