Issue #2247903 by bdone: Fixed Add a substr options to DedupeBase process plugin.

...modules/migrate/src/Plugin/migrate/process/DedupeBase.php

core/modules/migrate/tests/src/process/DedupeEntityTest.php

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

.../config/install/migrate.migration.d6_contact_category.yml

...pal/config/install/migrate.migration.d6_filter_format.yml

...nfig/install/migrate.migration.d6_taxonomy_vocabulary.yml

..._drupal/config/install/migrate.migration.d6_user_role.yml

.../migrate_drupal/src/Tests/Dump/Drupal6ContactCategory.php

...grate_drupal/src/Tests/Dump/Drupal6TaxonomyVocabulary.php

...modules/migrate_drupal/src/Tests/Dump/Drupal6UserRole.php

...igrate_drupal/src/Tests/d6/MigrateContactCategoryTest.php

...ate_drupal/src/Tests/d6/MigrateTaxonomyVocabularyTest.php

...dules/migrate_drupal/src/Tests/d6/MigrateUserRoleTest.php