This switches the dependency scanner from handling `Module` objects to
dealing with `serialization::ModuleFile`. Module file already contains
(almost) all of the information the scanner needs, and has the advantage
of not forcing deserialization of `Module` objects from PCM files, which
will become important in a later PR.
This alone improves clean scans by 1.8% and incremental scans by 2.6%.
This effect is likely caused by removing iteration over many `Module`
objects, removing deduplication via associative containers deduplication
of work, and sorting `Module` objects by name to ensure deterministic
order.
bf2b1efce5