[Issue 16020] Allow AliasDeclarationY to express function types

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=16020

Basile-z <b2.temp at gmx.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|AliasDeclarationY doesn't   |Allow AliasDeclarationY to
                   |allow to alias a function   |express function types
                   |type                        |

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