refactor: extract write_to_fd into util crate

Part of #12502

src/wutil/mod.rs

@@ -13,6 +13,7 @@
 use crate::signal::SigChecker;
 use crate::topic_monitor::Topic;
 use errno::errno;
+use fish_util::write_to_fd;
 use fish_wcstringutil::{join_strings, str2bytes_callback, wcs2bytes, wcs2osstring, wcs2zstring};
 use fish_widestring::{IntoCharIter, L, WExt as _, WString, wstr};
 use nix::unistd::AccessFlags;
@@ -351,10 +352,6 @@ pub fn wrename(old_name: &wstr, new_name: &wstr) -> io::Result<()> {
     fs::rename(old_narrow, new_narrow)
 }
 
-pub fn write_to_fd(input: &[u8], fd: RawFd) -> nix::Result<usize> {
-    nix::unistd::write(unsafe { BorrowedFd::borrow_raw(fd) }, input)
-}
-
 /// Write a wide string to a file descriptor. This avoids doing any additional allocation.
 /// Returns nothing when interrupted by ctrl-c or HUP.
 pub fn unescape_bytes_and_write_to_fd(input: impl IntoCharIter, fd: RawFd) -> Option<usize> {