Add YAML documentation for `fcntl.h` listing all functions and macros as defined in POSIX.1-2024 (IEEE Std 1003.1-2024). **Functions (6):** creat, fcntl, open, openat, posix_fadvise, posix_fallocate **Macros (51):** O_RDONLY, O_WRONLY, O_RDWR, O_APPEND, O_CREAT, O_EXCL, O_TRUNC, F_DUPFD, F_GETFD, F_SETFD, F_GETFL, F_SETFL, AT_FDCWD, POSIX_FADV_*, and more. Part of #122006