10 files declare their use of PluginBase in Feeds 8.3

DirectoryFetcher.php in src/Feeds/Fetcher/DirectoryFetcher.php

HttpFetcher.php in src/Feeds/Fetcher/HttpFetcher.php

OpmlParser.php in src/Feeds/Parser/OpmlParser.php

ParserBase.php in src/Feeds/Parser/ParserBase.php

ParserWithMappingForm.php in tests/modules/feeds_test_plugin/src/Feeds/Parser/ParserWithMappingForm.php

ProcessorBase.php in src/Feeds/Processor/ProcessorBase.php

SitemapParser.php in src/Feeds/Parser/SitemapParser.php

SourceBase.php in src/Plugin/Type/Source/SourceBase.php

SyndicationParser.php in src/Feeds/Parser/SyndicationParser.php

UploadFetcher.php in src/Feeds/Fetcher/UploadFetcher.php