[Issue 3075] Implement parameter contravariance

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=3075

--- Comment #32 from Bolpat <qs.il.paperinik at gmail.com> ---
Good:
```d
void main()
{
    void function(    const(int)*) fp = null;
    void function(          int *) gp = fp;
    void function(immutable(int)*) hp = fp;
}
```

Error:
```d
void main()
{
    void function(ref     const int ) fp = null;
    void function(ref           int ) gp = fp; // error
    void function(ref immutable(int)) hp = fp; // error
}
```

Same with s/function/delegate/g.

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