[perl #131948] Typename declared via type capture does not work in return type constraint

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# New Ticket Created by  Sam S. 
# Please include the string:  [perl #131948]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=131948 >


     ➜  sub f (::T --> T) { T.new }
     ➜  f Int;
     Died with X::TypeCheck::Return
       in sub f at [...]

The type alias T works just fine in the rest of the subroutine signature 
and body; just not inside the return type constraint, and also not in 
the return type constraint of any nested subroutine:

     ➜  sub f (::T) {  sub g (--> T) { T.new }  }
     ➜  say f(Int)();
     Died with X::TypeCheck::Return
       in sub g at [...]

The alternative `returns T` and `of T` syntaxes suffer from the same 
problem.