feat_wasm: add head to the WASM-compatible utilities

[sylvestre]

No description provided.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tty/tty-eof (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/pr/bounded-memory (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/cut/cut-huge-range is now passing!
Congrats! The gnu test tests/unexpand/bounded-memory is now passing!

[oech3]

   Compiling hashbrown v0.16.1
warning: ignoring -C extra-filename flag due to -o flag

error[E0433]: failed to resolve: could not find `unix` in `os`
   --> src/uucore/src/lib/features/fs.rs:786:18
    |
786 |     use std::os::unix::fs::MetadataExt;
    |                  ^^^^ could not find `unix` in `os`
    |
note: found an item that was configured out
   --> /rustc/6b00bc3880198600130e1cf62b8f8a93494488cc/library/std/src/os/mod.rs:36:9
note: the item is gated here
   --> /rustc/6b00bc3880198600130e1cf62b8f8a93494488cc/library/std/src/os/mod.rs:28:1
note: found an item that was configured out
   --> /rustc/6b00bc3880198600130e1cf62b8f8a93494488cc/library/std/src/os/mod.rs:85:9
note: the item is gated here
   --> /rustc/6b00bc3880198600130e1cf62b8f8a93494488cc/library/std/src/os/mod.rs:84:1

For more information about this error, try `rustc --explain E0433`.
warning: `uucore` (lib) generated 1 warning
error: could not compile `uucore` (lib) due to 1 previous error; 1 warning emitted

[sylvestre]

yeah, it is fixed by a previous PR