Issue 13052 - TypeInfo.getHash should return same hash for different floating point zeros

https://issues.dlang.org/show_bug.cgi?id=13052
I'm not sure about it too. It's equivalent with the code in old `TypeInfo_f.getHash()` member function.

And we don't have to consider about CTFE-ability. Currently TypeInfo.getHash is not always CTFE-able.