9 files declare their use of ActivityContextBase in Open Social 8

CommunityActivityContext.php in modules/custom/activity_basics/src/Plugin/ActivityContext/CommunityActivityContext.php

ContentInMyGroupActivityContext.php in modules/custom/activity_basics/src/Plugin/ActivityContext/ContentInMyGroupActivityContext.php

FollowContentActivityContext.php in modules/social_features/social_follow_content/src/Plugin/ActivityContext/FollowContentActivityContext.php

GroupActivityContext.php in modules/custom/activity_basics/src/Plugin/ActivityContext/GroupActivityContext.php

MentionActivityContext.php in modules/social_features/social_mentions/src/Plugin/ActivityContext/MentionActivityContext.php

OwnerActivityContext.php in modules/custom/activity_basics/src/Plugin/ActivityContext/OwnerActivityContext.php

PrivateMessageActivityContext.php in modules/social_features/social_private_message/src/Plugin/ActivityContext/PrivateMessageActivityContext.php

ProfileActivityContext.php in modules/custom/activity_basics/src/Plugin/ActivityContext/ProfileActivityContext.php

VoteActivityContext.php in modules/social_features/social_like/src/Plugin/ActivityContext/VoteActivityContext.php