Issue #2940169 by Nitebreed, jefuri, seanB: Remove all occurences of 'media entity' in core

core/modules/media/src/Annotation/MediaSource.php

core/modules/media/src/MediaAccessControlHandler.php

...c/Plugin/Field/FieldFormatter/MediaThumbnailFormatter.php

...modules/media/tests/src/Functional/MediaCacheTagsTest.php

...s/media/tests/src/Functional/MediaFunctionalTestTrait.php

core/modules/media/tests/src/Kernel/MediaKernelTestBase.php

...modules/media/tests/src/Kernel/MediaLinkRelationsTest.php

core/modules/media/tests/src/Kernel/MediaSourceTest.php

core/modules/media/tests/src/Kernel/MediaTest.php