A MigrationDeepFinderInterface is a MigrationFinderInterface, which locates migrations not only in a directory itself, but in subdirectories of this directory, too.
MigrationFinderInterface implementations locate migrations (classes that extend Doctrine\DBAL\Migrations\AbstractMigration) in a directory.
Generates Schema objects to be passed to the migrations class.
Generates Schema objects for the diff command. A schema provider should return the schema to which the database should be migrated.