Add `package_path` method to File type.

### Description of the feature request:

I would like a simple way to get the path of a file relative to the package it comes from.

Something like a method on File, that return the path relative to package directory that owns the file, or returns short_path if there is no owner.

### Which category does this issue belong to?

Core

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

The problem I ran into that caused me to want this is I am trying to create a zip file containing a python package. And I want the directory structure of the zip file to match the directory structure underneath the package where they python sources are contained. So I would like a way to get the path of a `File` relative to its owning package.

I think that there are probably also many other use cases for this as well .

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

linux

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

release 6.3.2

### 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 master; git rev-parse HEAD` ?

_No response_

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

not really, although it is kind of hard to search for.

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

It is possible to accomplish this in starlark with something like:

```starlark
path = f.short_path
if f.owner and path.startswith(f.owner.package + "/"):
path = path[len(f.owner.package) + 1:]
```

But that is very verbose, somewhat complicated, and not very discoverable. It took me quite a while to find that solution.

Start by locating Bazel's Starlark File type and the existing short_path, owner, and owner.package behavior. Add the requested package-relative path behavior, including the no-owner fallback described in the issue, then find or add focused coverage for both cases and verify the Starlark API result.

Written by the indexing model from the issue text.