Fix: Apply path traversal guard to WriteAllToZip() matching WriteAllToDisk() (#27171)

This PR applies the same path traversal guard already present in
`WriteAllToDisk()` to `WriteAllToZip()`. A plugin returning
a filename like `../../PWNED.txt` is blocked for directory output,
but currently slips silently into an archive, enabling Zip Slip-style entries.

This fix adds an identical `..` check and returns an error to prevent
traversal injection in .zip / .jar / .srcjar output.

Closes #27170

Closes #27171

COPYBARA_INTEGRATE_REVIEW=https://github.com/protocolbuffers/protobuf/pull/27171 from mrknight-n1du:main 95254bf142ae7be26cab82a6c51b63deb097b9d3
PiperOrigin-RevId: 911318632