[Issue 24540] Add order/index to enum member to return its position

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24540

--- Comment #1 from apham <apz28 at hotmail.com> ---
The value is also needed to be known at compile time

static assert(Foo.one.order == 0);
static assert(Foo.two.order == 1);

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