9 files declare their use of FileProcessorTrait in Backup and Migrate 8.4

CompressionFilter.php in lib/backup_migrate_core/src/Filter/CompressionFilter.php

DatabaseSource.php in lib/backup_migrate_core/src/Source/DatabaseSource.php

DrupalEncrypt.php in src/Filter/DrupalEncrypt.php

DrupalSiteArchiveSource.php in src/Source/DrupalSiteArchiveSource.php

FileDirectorySource.php in lib/backup_migrate_core/src/Source/FileDirectorySource.php

FileNamer.php in lib/backup_migrate_core/src/Filter/FileNamer.php

MetadataWriter.php in lib/backup_migrate_core/src/Filter/MetadataWriter.php

SidecarMetadataDestinationTrait.php in lib/backup_migrate_core/src/Destination/SidecarMetadataDestinationTrait.php

SourceBase.php in lib/backup_migrate_core/src/Source/SourceBase.php