[Sync EN] strpos: document that an empty needle matches at every position and returns the offset (#5856)

[github-actions]

Commit: https://github.com/php/doc-en/commit/dd5db7c6b22c45108b19ca815a0bdf07909bf14a
PR: https://github.com/php/doc-en/pull/5856

Archivos ES a actualizar

• reference/strings/functions/strpos.xml