Lucene schema index provider migrator for lossy->lossless numeric indexes

Only the affected indexes, and only affected documents actually, are updated
to the new long<-->double lossless representation.

In order to enable this kind of migration the store migration framework
had to be evolved quite a bit. Therefore StoreUpgrader is turned into the
controller of the whole migration process where participants can register
and are later on asked to determine whether or not migration for that
participant is required and if so asked to migrate. Participants can also
declare dependencies that other participants can satisfy.

Although whereas the dependency satisfication and resolution is in place,
that information is not used to reorder the participants, it's fixed to the
order they were added. That can be added later when we see fit.