Allows for iterating over the kvs when constructing with a list literal instead of having to create a separate array to pass into ComptimeStringMap in order to maintain access to the values.

For example when making a set, before in order to loop over the kvs you'd have to do something like:

    const MyKV = struct { @"0": []const u8 };
    const kvs: []const MyKV = &[_]MyKV{ .{ @"0" = "foo"}, .{ @"0" = "bar" } };
    const map = ComptimeStringMap(void, kvs);
    for (kvs) |kv| {}

whereas now it's possible to do:

    const map = ComptimeStringMap(void, .{ .{"foo"}, .{"bar"} });
    for (map.kvs) |kv| {}