Migrate lib/cpp2 from TARGETS to BUCK

Summary:
Migrate the rest of `lib/cpp2` from `TARGETS` to `BUCK`. This removes ~5 kLOC of duplicate build configs, a bunch of manually maintained dirsync rules and aligns with the future direction of `BUCK` adoption in fbcode: https://fb.workplace.com/groups/fbcode.fyi/posts/7176797622355977.

Unhack `server` and `quic_server` targets and improve compatibility between fbcode and xplat by moving fbcode-specific bit to `io_uring_util`.

Add target conversion for fizz.

Add missing headers to targets.

(Note: this ignores all push blocking failures!)

Reviewed By: avalonalex, thedavekwon

Differential Revision: D61018625

fbshipit-source-id: e64e91f8d370b158240d047bd04d6cf9aa34b359