Follow symlink support for `readdirp`

[mevatron]

I was attempt to use native-run on NixOS, and to make packages more reproducible the Nix package manager heavily uses symlinks :sweat_smile: Unfortunately, the readdirp method does not follow symlinks by default, and seeing as the @ionic/utils-fs package has many dependent projects, it seemed like making this a non-default option would be the best approach.

I added a WalkerOption followSymlinks and environment variable to also control the behavior IONIC_UTILS_FS_FOLLOW_SYMLINKS.

Would this be something that could be merged in?

Thanks!