Issue #2263453 by chx, benjy: Split migration_dependencies into two keys.

core/modules/migrate/lib/Drupal/migrate/MigrationStorage.php

.../Drupal/migrate/Plugin/migrate/destination/EntityFile.php

...l/config/install/migrate.migration.d6_aggregator_item.yml

...rate_drupal/config/install/migrate.migration.d6_block.yml

...grate_drupal/config/install/migrate.migration.d6_book.yml

...onfig/install/migrate.migration.d6_cck_field_revision.yml

.../config/install/migrate.migration.d6_cck_field_values.yml

...te_drupal/config/install/migrate.migration.d6_comment.yml

...g/install/migrate.migration.d6_comment_entity_display.yml

...tall/migrate.migration.d6_comment_entity_form_display.yml

...g/install/migrate.migration.d6_comment_field_instance.yml

...upal/config/install/migrate.migration.d6_custom_block.yml

...rate_drupal/config/install/migrate.migration.d6_field.yml

...install/migrate.migration.d6_field_formatter_settings.yml

...al/config/install/migrate.migration.d6_field_instance.yml

...l/migrate.migration.d6_field_instance_widget_settings.yml

...grate_drupal/config/install/migrate.migration.d6_file.yml

...grate_drupal/config/install/migrate.migration.d6_node.yml

...pal/config/install/migrate.migration.d6_node_revision.yml

...pal/config/install/migrate.migration.d6_node_settings.yml