TypeInfo.getHash(): use const scope

[WalterBright]

Start on making TypeInfo methods safe. Should be no problem since users won't be deriving from it.

[dlang-bot]

Thanks for your pull request, @WalterBright!

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[wilzbach]

Couldn't we fix in with -dip1000 to mean scope const again? At the moment in has become a bit useless ...

[wilzbach]

Why? Use of body has been deprecated in favor of do with https://github.com/dlang/DIPs/blob/master/DIPs/accepted/DIP1003.md

[WalterBright]

I don't think we can fix in. It may break an astonishing amount of code, since it was never enforced.

[dnadlinger]

Erm, sure, this change is probably benign, but how do you expect to ever make getHash @safe? The fact that it dereferences a void* will remain a giant safety hole, and we should be transitioning to making it @system instead.