Offer a way to get a provider from ctx.super() response

### Description of the feature request:

The response from `ctx.super()` contains the providers returned by the parent rule, and it is possible to get these by indexing the returned value. However, there is no easy way to get a particular provider from the response. Native providers can be found by looking at the type of each provider, but custom providers simply show up as a struct.

### Which category does this issue belong to?

Rules API

### What underlying problem are you trying to solve with this feature?

I need to get a field from one of the providers returned by the parent rule.

### Which operating system are you running Bazel on?

_No response_

### What is the output of `bazel info release`?

8.4.0

### If `bazel info release` returns `development version` or `(@non-git)`, tell us how you built Bazel.

_No response_

### What's the output of `git remote get-url origin; git rev-parse HEAD` ?

```text

```

### Have you found anything relevant by searching the web?

_No response_

### Any other information, logs, or outputs that you want to share?

_No response_

The issue names the Rules API and ctx.super(); begin by locating the implementation and tests for ctx.super() and provider access. Compare how native and custom providers are represented, then define and test how a specific provider can be selected and its field retrieved.

Written by the indexing model from the issue text.