implement randomize for QueryIter

[Victoronz]

Objective

There is no out of the box way to randomize query iteration order. While order is currently not guaranteed, it is still deterministic.

Closes #14393

Solution

Implement a randomize method for QueryIter. This uses a cached sort of Entity with its hash as the key.
Since the underlying implementation is just a sort, it returns a type alias of QuerySortedIter, named QueryRandomIter.
The same could be done for QueryManyIter if #13443 merges.

Testing

The example acts as a doc test.

Showcase

Fetch 7 random query items!
let random_items = query.iter().randomize().take(7);

[alice-i-cecile]

While I really like randomizing query orders for gameplay reasons, I don't think we should add this: randomization without a seed is a serious source of tech debt. See #2504 for some previous discussion.

We could provide a better API by passing in an RNG, but that adds a dependency for pretty niche functionality. Ultimately I think the linked issue is better closed with an example, unless we want to add a full entropy / RNG solution.

[Victoronz]

makes sense, this method is a simple convenience, and if there are serious implications to adding this to bevy itself, then it is better to have the implementation fall on the user.
Maybe it makes sense to have a query_sorts example file to show this and some other applications?

[alice-i-cecile]

I would call it sorting_queries, but yeah :)