ctx.fragments.apple.{multi_arch_platform,get_split_build_configs}() are removed, even though they're still used

### Description of the bug:

From this commit: https://github.com/bazelbuild/bazel/commit/ed2472981c4ea6aab0046cec44cf31d1137c9342

> Remove ctx.fragments.apple.multi_arch_platform
> It was unused except for tests.

This is not correct. It's used by rules_apple@master:

https://github.com/bazelbuild/rules_apple/blob/f37305163dd7546f87839f3187e153c955cd20d8/apple/internal/platform_support.bzl#L96

### Which category does this issue belong to?

C++ Rules

### What's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

Use the latest rules_apple in combination with Bazel 9.0.0rc1.

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

macOS

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

9.0.0rc1

### 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

```

### If this is a regression, please try to identify the Bazel commit where the bug was introduced with bazelisk --bisect.

_No response_

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

_No response_

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

The documentation for single_arch_platform still refers to multi_arch_platform. The link for it is now broken. https://bazel.build/rules/lib/fragments/apple

Start with the referenced rules_apple apple/internal/platform_support.bzl usage and the Bazel commit that removed the APIs. Check the Apple fragment documentation at bazel.build/rules/lib/fragments/apple; done means the methods remain usable by the latest rules_apple and the single_arch_platform documentation no longer links to a removed API.

Written by the indexing model from the issue text.