Write EntityResourceTestBase subclasses for every other entity type.

This is a follow-up for #2737719: EntityResource: Provide comprehensive test coverage: for every entity type, every format, every method.

It was deemed wiser to only apply this new test coverage to all entity types that already had some test coverage in the existing REST tests: Node, User, Term, EntityTest, Comment, Block, ConfigTest, Role and Vocabulary.
All other entity types are deferred to a follow-up […]

This is that follow-up.

Entity types to add test coverage for here:

Content entity types

1. MenuLinkContent: #2832859: Write EntityResourceTestBase subclasses for: MenuLinkContentAssigned to: webflo
2. BlockContent: #2835845: EntityResource: Provide comprehensive test coverage for BlockContent entityAssigned to: arshadcn
3. File: #2843139: EntityResource: Provide comprehensive test coverage for File entity
4. Shortcut: #2843750: EntityResource: Provide comprehensive test coverage for Shortcut entityAssigned to: sumanthkumarc
5. Item: #2843752: EntityResource: Provide comprehensive test coverage for Item entity
6. ContentModerationState: #2843753: EntityResource: Provide comprehensive test coverage for ContentModerationState entity
7. Feed: #2843754: EntityResource: Provide comprehensive test coverage for Feed entity
8. Message: #2843755: Allow Message entities to be created (i.e. contact forms to be sent) via REST (was: "EntityResource: Provide comprehensive test coverage for Message entity")

Config entity types

1. FieldStorageConfig: #2843756: EntityResource: Provide comprehensive test coverage for FieldStorageConfig entity
2. FilterFormat: #2843757: EntityResource: Provide comprehensive test coverage for FilterFormat entity
3. View: #2843758: EntityResource: Provide comprehensive test coverage for View entity
4. SearchPage: #2843759: EntityResource: Provide comprehensive test coverage for SearchPage entity
5. ConfigurableLanguage: #2843761: EntityResource: Provide comprehensive test coverage for ConfigurableLanguage entity
6. Action: #2843762: EntityResource: Provide comprehensive test coverage for Action entityAssigned to: sumanthkumarc
7. ContentLanguageSettings: #2843763: EntityResource: Provide comprehensive test coverage for ContentLanguageSettings entity
8. EntityFormDisplay: #2843764: EntityResource: Provide comprehensive test coverage for EntityFormDisplay entity
9. EntityViewDisplay: #2843765: EntityResource: Provide comprehensive test coverage for EntityViewDisplay entity
10. FieldConfig: #2843766: EntityResource: Provide comprehensive test coverage for FieldConfig entity
11. BaseFieldOverride: #2843767: EntityResource: Provide comprehensive test coverage for BaseFieldOverride entity
12. Tour: #2843768: EntityResource: Provide comprehensive test coverage for Tour entityAssigned to: sumanthkumarc
13. ResponsiveImageStyle: #2843770: EntityResource: Provide comprehensive test coverage for ResponsiveImageStyle entity
14. RdfMapping: #2843771: EntityResource: Provide comprehensive test coverage for RdfMapping entity
15. DateFormat: #2843772: EntityResource: Provide comprehensive test coverage for DateFormat entity
16. RestResourceConfig: #2843773: EntityResource: Provide comprehensive test coverage for RestResourceConfig entity
17. BlockContentType: #2843774: EntityResource: Provide comprehensive test coverage for BlockContentType entity
18. CommentType: #2843775: EntityResource: Provide comprehensive test coverage for CommentType entity
19. EntityTestBundle: #2843776: EntityResource: Provide comprehensive test coverage for EntityTestBundle entity
20. NodeType: #2843777: EntityResource: Provide comprehensive test coverage for NodeType entity
21. ContactForm: #2843778: EntityResource: Provide comprehensive test coverage for ContactForm entityAssigned to: sumanthkumarc
22. ShortcutSet: #2843779: EntityResource: Provide comprehensive test coverage for ShortcutSet entityAssigned to: sumanthkumarc
23. EntityFormMode: #2843780: EntityResource: Provide comprehensive test coverage for EntityFormMode entity
24. EntityViewMode: #2843781: EntityResource: Provide comprehensive test coverage for EntityViewMode entity
25. Editor: #2843782: EntityResource: Provide comprehensive test coverage for Editor entity
26. Menu: #2843783: EntityResource: Provide comprehensive test coverage for Menu entity
27. ModerationStateTransition: #2843784: EntityResource: Provide comprehensive test coverage for ModerationStateTransition entity
28. ModerationState: #2843785: EntityResource: Provide comprehensive test coverage for ModerationState entity
29. ImageStyle: #2843786: EntityResource: Provide comprehensive test coverage for ImageStyle entity