Issue #2910883 by vaplas, ShawnB, Wim Leers: Move all entity type REST tests to the providing modules

Issue #2835845 by vaplas, Wim Leers, arshadcn, Berdir: EntityResource: Provide comprehensive test coverage for BlockContent entity

Issue #2832859 by vaplas, webflo, harings_rob, Wim Leers: Write EntityResourceTestBase subclasses for: MenuLinkContent

Issue #2113345 by dawehner, tedbow, Wim Leers, kristiaanvandeneynde, Crell, Grayside, klausi: Define a mechanism for custom link relationships

Issue #2805281 by Wim Leers, damiankloip: ?_format=hal_json error responses are application/json, yet should be application/hal+json

Issue #2737719 by Wim Leers, dawehner: EntityResource: Provide comprehensive test coverage: for every entity type, every format, every method

Revert "Issue #2737719 by Wim Leers, dawehner: EntityResource: Provide comprehensive test coverage: for every entity type, every format, every method"

This reverts commit 59781ffc.

Issue #2737719 by Wim Leers, dawehner: EntityResource: Provide comprehensive test coverage: for every entity type, every format, every method