[Issue 14680] Investigate the use of .di files for Phobos

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=14680
Issue 14680 depends on issue 14694, which changed state.

Issue 14694 Summary: Functions nested within functions need their body in the generated .di file
https://issues.dlang.org/show_bug.cgi?id=14694

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

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