Search runfiles in `select_file` rule

`select_file` rule currently only searches within `DefaultInfo.files`.

I was wondering if we can add an argument to `select_file` to optionally expand the search criteria to include `DefaultInfo.default_runfiles`

It would look something like this.
```starlark
select_file(
name = "selected",
srcs = ":files",
subpath = "foo/bar.py",
include_runfiles = True,
)
```

Start by locating the `select_file` rule and tracing how it searches `DefaultInfo.files`. Determine how an optional `include_runfiles = True` setting should include `DefaultInfo.default_runfiles`, then verify that the example selecting `foo/bar.py` works when the file exists only in runfiles while existing behavior remains unchanged.

Written by the indexing model from the issue text.