Add missing Fanotify APIs from the libc crate into Nix.

[carlvoller]

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What does this PR do

Adds support for nix to receive additional Fanotify information records (such as libc::fanotify_event_info_fid, libc::fanotify_event_info_error and libc::fanotify_event_info_pidfd) Adds abstractions over the new fanotify structs. Adds new InitFlags to allow receiving these new information records.

This closes #2551

Checklist:

• [x] I have read CONTRIBUTING.md
• [x] I have written necessary tests and rustdoc comments
• [x] A change log has been added if this PR modifies nix's API