[Issue 11616] Introduce virtual keyword and remove virtual-by-default

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=11616
Issue 11616 depends on issue 12801, which changed state.

Issue 12801 Summary: "virtual" keyword added to compiler without being added to language specification
https://issues.dlang.org/show_bug.cgi?id=12801

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

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