mv,cp: fix xattr TOCTOU by using file descriptor-based operations

[sylvestre]

Closes: #10014

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/cp/cp-mv-enotsup-xattr. tests/cp/cp-mv-enotsup-xattr is passing on 'main'. Maybe you have to rebase?

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/cp/cp-mv-enotsup-xattr. tests/cp/cp-mv-enotsup-xattr is passing on 'main'. Maybe you have to rebase?

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/cp/cp-mv-enotsup-xattr. tests/cp/cp-mv-enotsup-xattr is passing on 'main'. Maybe you have to rebase?
Note: The gnu test tests/cp/sparse-2 is now being skipped but was previously passing.

[codspeed-hq]

Merging this PR will not alter performance

✅ 288 untouched benchmarks
⏩ 40 skipped benchmarks¹

---

_{Comparing sylvestre:issue-10014 (c857f11) with main (2f38180)}

Footnotes

1. 40 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/cp/cp-mv-enotsup-xattr. tests/cp/cp-mv-enotsup-xattr is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cp/existing-perm-race. tests/cp/existing-perm-race is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cp/file-perm-race. tests/cp/file-perm-race is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/date/date-locale-hour. tests/date/date-locale-hour is passing on 'main'. Maybe you have to rebase?

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/cp/cp-mv-enotsup-xattr. tests/cp/cp-mv-enotsup-xattr is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cp/existing-perm-race. tests/cp/existing-perm-race is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cp/file-perm-race. tests/cp/file-perm-race is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/date/date-locale-hour. tests/date/date-locale-hour is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/date/resolution. tests/date/resolution is passing on 'main'. Maybe you have to rebase?

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/cp/cp-mv-enotsup-xattr. tests/cp/cp-mv-enotsup-xattr is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cp/existing-perm-race. tests/cp/existing-perm-race is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cp/file-perm-race. tests/cp/file-perm-race is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/tty/tty-eof (fails in this run but passes in the 'main' branch)

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/cp/cp-mv-enotsup-xattr. tests/cp/cp-mv-enotsup-xattr is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cp/existing-perm-race. tests/cp/existing-perm-race is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cp/file-perm-race. tests/cp/file-perm-race is passing on 'main'. Maybe you have to rebase?