One step out of the TypeInfo stalemate

[rikki cattermole]

On 30/07/2020 5:36 AM, Paul Backus wrote:
> The main disadvantage of using TypeInfo for this is that it doesn't work 
> without the D runtime (i.e., in BetterC).

If it is templated with the type which then generates the member fields 
of the TypeInfo, this doesn't matter.

It is no longer the responsibility of the compiler to emit the TypeInfo 
members, and it can be on demand even if druntime is not linked in.