Replace DummyInternalVersion with mocking object to make test conditi…

[wx930910]

Fixes #JCR-4710 Refactor DummyInternalVersion in VersionIteratorImplTest.java to improve test logic.

Description

Refactor test class VersionIteratorImplTest.java

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Motivation

• Decoupling test class DummyInternalVersion from production interface InternalVersion.
• Making test condition more clear by removing all redundant overridden methods.
• Making test logic more clear by using method stub instead of method overriding.

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Key changed/added classes in this PR

• Created mocking object to replace test subclass DummyInternalVersion, decoupled test from production code.
• Created a method that return the mocking object for reuse purpose.
• Use method stub to replace method overriding to control mocking object's behavior.
• Remove redundant overridden methods to improve test logic.

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