fs: clean up Dir.read() uv_fs_t data before calling into JS

A call into JS can schedule another operation on the same `uv_dir_t`.
In particular, when the handle is closed from the callback for a
directory read operation, there previously was a race condition window:

1. A `dir.read()` operation is submitted to libuv
2. The read operation is finished by libuv, calling `AfterDirRead()`
3. We call into JS
4. JS calls dir.close()
5. libuv posts the close request to a thread in the pool
6. The close request runs, destroying the directory handle
7. `AfterDirRead()` is being exited.

Exiting the `FSReqAfterScope` in step 7 attempts to destroy the original
uv_fs_t` from step 1, which now points to an `uv_dir_t` that has
already been destroyed in step 5.

By forcing the `FSReqAfterScope` to clean up before we call into JS,
we can be sure that no other operations on the same `uv_dir_t` are
submitted concurrently.

This addresses issues observed when running with ASAN/valgrind.

PR-URL: https://github.com/nodejs/node/pull/33274


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>