zig: Temporarily roll back changes depending on new extension API (#13709)

This PR temporarily rolls back the changes in #12173 so that we can
publish a new version of the Zig extension.

There was a problem stemming from #12614 that caused v0.1.2 of the Zig
extension to get re-published with unreleased `zed_extension_api`
changes.

Once we publish v0.1.3 we'll be able to revert this change.

Release Notes:

- N/A