Originally the `JoinDependency` has the deduplication for eager loading
(LEFT JOIN). This re-uses that deduplication for `left_joins`.

And also, This makes left join order into part of joins, i.e.:

Before:

```
association joins -> stash joins (eager loading, etc) -> string joins -> left joins
```

After:

```
association joins -> stash joins (eager loading, left joins, etc) -> string joins
```

Now string joins are able to refer left joins.

Fixes #34325.
Fixes #34332.
Fixes #34536.