The `lib_link` callback cannot always be fully replaced/removed, as in
some case it is also doing some validation checks, or data editing based
on the result of lib_linking internal ID pointers.
The callback has been renamed for that purpose, from `read_lib` to
`read_after_liblink`. It is now called after all ID pointers have been
fully lib-linked for the current ID, but still before the call to
`do_versions_after_linking`.
This change should not have any behavioral effect. Although in theory
the side-effect of this commit (to split lib linking itself, and the
validation/further processing code) into two completely separated steps
could have some effects, in practice none are expected, and tests did
not show any changes in behavior either..
Part of implementing #105134: Removal of readfile's lib_link & expand code.
b53c7a804a