Fix `@length`-constrained collection shapes whose members are not constrained (#2103)

* Fix `@length`-constrained collection shapes whose members are not constrained

The generated code these should have emitted was fixed in #2085 (it's
bug number 2), but code generation is still crashing because the call to
calculate the inner constraint violation symbol is performed _before_
checking that the collection's member can reach a constrained shape.

The test that #2085 added in `constraints.smithy`:

```smithy
@length(max: 69)
list LengthList {
    member: ConB
}
```

was not exercising what it should have, since `ConB`, is its name hints
at, is a constrained structure shape.

* Add changelog entry

Co-authored-by: Julian Antonielli <julianantonielli@gmail.com>