Add variants of `pipe()`, and `duplicate()` that wrap `pipe2` and `dup3`

[jakepetroules]

pipe2() and dup3() were standardized by POSIX 2024 and are already supported on most platforms (Linux, BSD) outside of macOS.

We should add new overloads of the Swift System functions which accept the flags (like O_CLOEXEC). For Apple platforms, which don't support these calls, we could compile them out for now, throw an error, or add unavailable annotations.

[glessard]

Jake's forum pitch and thread: https://forums.swift.org/t/pitch-swiftsystem-dup3-and-pipe2-cover-apis/