chore: split ImportDataConverter into multiple classes and add unit testing (#33394)

apps/meteor/app/importer-csv/server/CsvImporter.ts

...er-hipchat-enterprise/server/HipChatEnterpriseImporter.js

.../app/importer-pending-files/server/PendingFileImporter.ts

...eor/app/importer-slack-users/server/SlackUsersImporter.ts

...meteor/app/importer/server/classes/ImportDataConverter.ts

apps/meteor/app/importer/server/classes/Importer.ts

...eteor/app/importer/server/classes/VirtualDataConverter.ts

.../app/importer/server/classes/converters/ConverterCache.ts

...pp/importer/server/classes/converters/MessageConverter.ts

...app/importer/server/classes/converters/RecordConverter.ts

...r/app/importer/server/classes/converters/RoomConverter.ts

...r/app/importer/server/classes/converters/UserConverter.ts

apps/meteor/ee/server/lib/ldap/Manager.ts

apps/meteor/server/lib/ldap/Manager.ts

apps/meteor/server/lib/ldap/UserConverter.ts

...r/tests/unit/app/importer/server/messageConverter.spec.ts

...or/tests/unit/app/importer/server/recordConverter.spec.ts

...teor/tests/unit/app/importer/server/roomConverter.spec.ts

...teor/tests/unit/app/importer/server/userConverter.spec.ts