[Issue 23907] New: __traits(child) respects visibility

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23907

          Issue ID: 23907
           Summary: __traits(child) respects visibility
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: qs.il.paperinik at gmail.com

The `child` trait is a reflection tool. It should **not** respect visibility
(in the second parameter, i.e. the alias of a member function). If respecting
visibility is desired, `getVisibility` can be used. This is consistent with
other reflection traits, the reason being that a library that uses reflection
may be passed a private symbol in the module in which it is defined.

Visibility is (correctly) bypassed when the address of the expression is taken.

Example (suitable for run.dlang.io):
```d
--- a.d
module a;

struct S
{
    private void f(int i)
    {
        import std.stdio;
        writeln("S.f(", i, ")");
    }
}

alias publicAlias = S.f;

--- playground.d
#line 17 "playground.d"

import a;

void main()
{
    S s;
    s.f(0); // okay: fails because `f` is private
    __traits(child, s, publicAlias)(42); // bug: fails
    (&__traits(child, s, publicAlias))(42); // okay
}
```d

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