fix Bson.opEquals: order of object keys is not determined

[IgorStepanov]

Subj. This PR is needed for druntime#2243
If it is possible, make a new tag if this will be approved, please.

[IgorStepanov]

Looks like that fail unrelated with this PR.

[wilzbach]

Yes, Vibe.d currently doesn't compile with 2.081. A new patch release is under its way.

[IgorStepanov]

Ping

[wilzbach]

Ping @s-ludwig - are you okay with this?
BTW doesn't suffer the Json implementation from the same flaw?

[wilzbach]

(going to merge this if there are no objections within the next 72h)

[s-ludwig]

I wonder what the correct approach here is, or whether there is one (the spec doesn't seem to be helpful). It could be argued that the order is part of the semantics. In fact, MongoDB appears to compare objects including their order.

[wilzbach]

I wonder what the correct approach here is, or whether there is one (the spec doesn't seem to be helpful). It could be argued that the order is part of the semantics. I

The spec is pretty clear on that:

Implementation Defined: The built-in associative arrays do not preserve the order of the keys inserted into the array. In particular, in a foreach loop the order in which the elements are iterated is typically unspecified.

https://dlang.org/spec/hash-map.html

Of course, it might make sense for Bson to have a defined order, but you can't rely on built-in arrays for this.

[IgorStepanov]

@s-ludwig @wilzbach ping.

@s-ludwig, If we want to create Bson implementation which preserve fields order, we should rewrite Bson and don`t use associative array anywhere. This PR fixes univocal trouble of current implementation.

[wilzbach]

As releasing a new version is a bit more difficult for Vibe.d, I set the version to be tested at the project tester to master: dlang/ci#241