[Issue 18918] New: core.internal.hash should perform memberwise hashing of structs with references

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18918

          Issue ID: 18918
           Summary: core.internal.hash should perform memberwise hashing
                    of structs with references
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: druntime
          Assignee: nobody at puremagic.com
          Reporter: n8sh.secondary at hotmail.com

So the following passes:

```d
unittest
{
    static struct S { char[] array; }
    auto s1 = S("abc".dup);
    auto s2 = S(s1.array.dup);
    import core.internal.hash : hashOf;
    assert(hashOf(s1) == hashOf(s2));

```

The eventual goal is to make core.internal.hash usable as a replacement for
`typeid(x).getHash(&x)` that doesn't require runtime type info (useful for
`betterC`) and doesn't ignore `const`-correctness.

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