Efficient way to relocate files in runfiles

### Description of the feature request:

There are situations where having more granular control over the layout of files and directories in runfiles is beneficial.

## Python context

Specifically, for rules_python, when we import third_party wheels (archives) from indexes like PyPI (Python Package Index), we would ideally like to expand the archives into a directory called `site-packages`. This is because outside the bazel context, packages are expanded as siblings inside `site-packages`.

This creates a major impedance mismatch between bazel and archives or foreign packages brought in from other ecosystems. It truly breaks assumptions in breaking ways in Python. One example (there are many others): NVIDIA wheels are expected to be installed as siblings of site-packages and they even have relative `RPATH` inside their `.so`. There are no built-in mechanisms to solve this cleanly in Python or bazel at the moment. See https://github.com/bazelbuild/rules_python/issues/2156

Here is a typical example of the contents of `site-packages` for `pip install requests` where you can see the standard layout when not using bazel.

```
tree -L 1 .venv/lib/python3.9/site-packages/ 20:49:03
.venv/lib/python3.9/site-packages/
├── _distutils_hack
├── certifi
├── certifi-2024.8.30.dist-info
├── charset_normalizer
├── charset_normalizer-3.3.2.dist-info
├── distutils-precedence.pth
├── idna
├── idna-3.10.dist-info
├── pip
├── pip-22.0.4.dist-info
├── pkg_resources
├── requests
├── requests-2.32.3.dist-info
├── setuptools
├── setuptools-58.1.0.dist-info
├── urllib3
└── urllib3-2.2.3.dist-info
```

## Other contexts

This is more than just a Python problem. Node has similar challenges with `node_modules`.

cc @rickeylev @fmeum

### Which category does this issue belong to?

_No response_

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

_No response_

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

All

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

N/A

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

N/A

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

```text
N/A
```

### 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 request concerns Bazel runfiles layout, especially expanding Python wheels under site-packages, and references rules_python issue #2156. Start by reviewing runfiles handling and that linked issue; done means a supported way to relocate files or directories while preserving the required package layout, with coverage for the stated Python use case.

Written by the indexing model from the issue text.