If the flag --incompatible_no_implicit_file_export is enabled, files that are implicitly exported because they are mentioned in the BUILD have private visibility regardless of the default visibility of the package.

Migration: add an explicit exports_files for all files that should be used outside the package they belong to.

Design document: https://github.com/bazelbuild/proposals/blob/master/designs/2019-10-24-file-visibility.md