HHH-9261 : Backport HHH-9106 to 4.2 (Multiple representations of the same entity cannot be merged using cascade=merge)
HHH-9261 :  Backport HHH-9106 to 4.2 (Multiple representations of the same entity cannot be merged using cascade=merge)

(cherry picked from commit 6203b5da308ad45167ad0cbcc44214433b4e7f7b)

Conflicts:
	hibernate-core/src/main/java/org/hibernate/boot/registry/selector/internal/StrategySelectorBuilder.java
	hibernate-core/src/main/java/org/hibernate/event/internal/EntityCopyAllowedObserver.java
	hibernate-entitymanager/src/test/java/org/hibernate/jpa/test/emops/MergeMultipleEntityRepresentationsAllowedTest.java
HHH-9261 : Backport HHH-9106 to 4.2 (Multiple representations of the same entity cannot be merged using cascade=merge)

(cherry picked from commit 368cdc1966b2018e03a3a5a0a6cf420a9939c398)

Conflicts:
	hibernate-entitymanager/src/test/java/org/hibernate/jpa/test/emops/MergeMultipleEntityCopiesDisallowedByDefaultTest.java
HHH-9261 :  Backport HHH-9106 to 4.2 (Multiple representations of the same entity cannot be merged using cascade=merge)

(cherry picked from commit 31bcb0ea0a73c32bbb430ac6eed54005f01a40f2)
HHH-9261 :  Backport HHH-9106 to 4.2 (Multiple representations of the same entity cannot be merged using cascade=merge)