Transition to exec configuration for `bazel run --run_under=... --platforms=...`

### Description of the bug:

This is closely related to https://github.com/bazelbuild/bazel/issues/22624.

That issue (now fixed) was about transitioning to the exec configuration when `bazel test --run_under=... --platforms=...` is invoked.

The same behavior should apply to `bazel run` as to `bazel test`, but currently does not: the `--run_under` binary is built for the target platform, even though it is then immediately executed on the exec platform. There's actually a TODO to handle this (added by @katre in https://github.com/katre/bazel/commit/b03e4c5e4df4728b943945370141c047b9d98039), but I don't believe there was a tracking issue before.

The context in which this bit us this week is trying to run a binary in emulation. We build the binary for an embedded platform (by setting `--platforms`) and then use `--run_under` to run it under [QEMU](https://www.qemu.org/). But this does not work as expected, because Bazel tries to build the emulator itself for the embedded platform!

### Which category does this issue belong to?

Configurability

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

_No response_

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

Linux

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

8.1.0

### 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

```

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

No

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

_No response_

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

_No response_