[Issue 18110] most of phobos should be @safe-ly useable

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18110
Issue 18110 depends on issue 14439, which changed state.

Issue 14439 Summary: aa's keys, values not usable in @safe context
https://issues.dlang.org/show_bug.cgi?id=14439

           What    |Removed                     |Added
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             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

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