Looking for a "join-like" or "lookup-like" expression.

Hello,

First and foremost, thanks in advance for sharing JMESPath which I find very elegant and powerful.

I have recently been faced with a challenge for which I could not build a single JMESPath expression that solves it for me. Consider the case of a JSON document like:

```
{
"things": [{
"id": 1,
"name": "Thing #1",
"owner_id": 1
}, {
"id": 2,
"name": "Thing #2",
"owner_id": 2
}, {
"id": 3,
"name": "Thing #3",
"owner_id": 1
}],
"users": [{
"id": 1,
"name": "User #1"
}, {
"id": 2,
"name": "User #2"
}]
}
```

The objective would be to return a the list of `things` where each `owner_id` wold be "resolved", so to speak, from the entries in the `users` array. To put it In SQL-ish terms, I'm looking to join `things` and `users` on `things[*].owner_id` and `users[*].id`.

After trying multiple things, the best and cleanest (albeit non-working!) solution I came up with was something like:

```
things[*].{id: id, owner_id:owner_id, owner:users[?id == owner_id]}
```

Unfortunatelly, within the multiselect hash, the expression for `owner` can't resolve `users`. It's clearly a matter of scope. Having investigated furter, I found out about JEP 11 https://github.com/jmespath/jmespath.site/pull/6 and it seems like the `let` function could be a possible solution.

Facts:
* I could create a custom function to handle my particular need.
* With JEP 11 in place, I could build an expression to solve this particular challenge.

Other than those two options, am I missing something that could be used currently?

Thanks in advance.
Regards.