Revert "loader/lua: Remove pager shim"

This reverts commit 8b9178cd0d35ff2beafebdd51c8c44ba2b5aeb0f.

Really old loader.efi files persist in the field. Revert this to support
it. We need to support this through at least 14.2 now, alas.

MFC After: 3 days
Sponsored by: Netflix
Reviewed by: kevans
Differential Revision: https://reviews.freebsd.org/D45881

(cherry picked from commit b38a82c77ab90eace53c56151b191efd1f4a8439)