[Issue 12615] Warn against, and then deprecate old alias syntax

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=12615
Issue 12615 depends on issue 12802, which changed state.

Issue 12802 Summary: Allow optional 'StorageClasses' for new alias syntax
https://issues.dlang.org/show_bug.cgi?id=12802

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

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