SGA Core naming inconsistency meta2def vs build_file_meta

[ModernMAK]

When writing we have meta2def but reading lacks a def2meta handler.

This currently prevents any SGA aside from V2 from creating proper EssenceFS objects.

Two separate naming conventions, one should be refactored to match the other.

Alternatively, using a class to group the strategies together, which would make it easier to create the serializers.

[ModernMAK]

Callables are nice; but having a proper protocol class would make things easier, something like InfoConverter (T <-> Dict[str,Object])? Since FS internally refers to the files' / filesystems' metadata as Info.

Also standardizing the nomenclature for these files' layout would be helpful; but that deserves its own issue.