buildifier does not move package() to the top in some cases

if you have a BUILD file like this:

```bzl
some_target(
...
)

some_list = [
#
]

package(default_visibility = ["//visibility:public"])
```

buildifier does not warn about the package() being at the bottom, nor does it move it to the top when fixing

Start by running buildifier on the provided BUILD file, with package() after a target and list, and compare checking with fixing. Trace the package-ordering behavior from the buildifier entry point. Done means buildifier warns about the misplaced package() call and moves it to the top when fixing.

Written by the indexing model from the issue text.