[Issue 11747] Better error message with @disabled toString

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=11747
Issue 11747 depends on issue 18149, which changed state.

Issue 18149 Summary: Add a compiler trait to detect if a function is @disable
https://issues.dlang.org/show_bug.cgi?id=18149

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

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