[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 18168, which changed state.

Issue 18168 Summary: std.base64.encode for output ranges should be usable in @safe
https://issues.dlang.org/show_bug.cgi?id=18168

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

--