[Issue 21143] New: vtbl not accessible without typeid

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21143

          Issue ID: 21143
           Summary: vtbl not accessible without typeid
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: andrei at erdani.com

__traits(vptr) returns the vptr, but there's no size information so the vtbl is
not availale. There should be a trait for that.

This blocks https://github.com/dlang/druntime/pull/3174.

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