[Issue 21183] New: schwartzSort does not strip const

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21183

          Issue ID: 21183
           Summary: schwartzSort does not strip const
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: minor
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: default_357-line at yahoo.de

Consider the following code:

import std.algorithm : schwartzSort;
import std.array : array;

struct S
{
    int i;
    const(int) foo() { return i; }
}

void main()
{
    auto list = [S(4), S(3), S(2)];
    assert(list.dup.schwartzSort!(a => a.foo).array == [S(2), S(3), S(4)]);
}

This leads to cryptic errors due to the fact that `schwartzSort` does not strip
the `const` from `const(int)` for its internal array, even though it trivially
could since it's a value type.

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