[Issue 21169] make checkedint as a drop-in replacement of native int/long

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21169
Issue 21169 depends on issue 18024, which changed state.

Issue 18024 Summary: checkedint.Abort and checkedint.Warn should be @safe
https://issues.dlang.org/show_bug.cgi?id=18024

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

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