21 files declare their use of ProcessorPluginBase in Facets 8

BooleanItemProcessor.php in src/Plugin/facets/processor/BooleanItemProcessor.php

CountLimitProcessor.php in src/Plugin/facets/processor/CountLimitProcessor.php

DateItemProcessor.php in src/Plugin/facets/processor/DateItemProcessor.php

DependentFacetProcessor.php in src/Plugin/facets/processor/DependentFacetProcessor.php

ExcludeSpecifiedItemsProcessor.php in src/Plugin/facets/processor/ExcludeSpecifiedItemsProcessor.php

GranularItemProcessor.php in src/Plugin/facets/processor/GranularItemProcessor.php

HideActiveItemsProcessor.php in src/Plugin/facets/processor/HideActiveItemsProcessor.php

HideNonNarrowingResultProcessor.php in src/Plugin/facets/processor/HideNonNarrowingResultProcessor.php

HideOnlyOneItemProcessor.php in src/Plugin/facets/processor/HideOnlyOneItemProcessor.php

HierarchyPluginBase.php in src/Hierarchy/HierarchyPluginBase.php

InvalidQT.php in tests/facets_custom_widget/src/Plugin/facets/processor/InvalidQT.php

ListItemProcessor.php in src/Plugin/facets/processor/ListItemProcessor.php

ShowOnlyDeepestLevelItemsProcessor.php in src/Plugin/facets/processor/ShowOnlyDeepestLevelItemsProcessor.php

ShowSiblingsProcessor.php in src/Plugin/facets/processor/ShowSiblingsProcessor.php

SliderProcessor.php in modules/facets_range_widget/src/Plugin/facets/processor/SliderProcessor.php

TestPreQuery.php in tests/facets_custom_widget/src/Plugin/facets/processor/TestPreQuery.php

TranslateEntityAggregatedFieldProcessor.php in src/Plugin/facets/processor/TranslateEntityAggregatedFieldProcessor.php

TranslateEntityProcessor.php in src/Plugin/facets/processor/TranslateEntityProcessor.php

UidToUserNameCallbackProcessor.php in src/Plugin/facets/processor/UidToUserNameCallbackProcessor.php

UrlProcessorHandler.php in src/Plugin/facets/processor/UrlProcessorHandler.php

UrlProcessorPluginBase.php in src/UrlProcessor/UrlProcessorPluginBase.php