Exclude manifest classes from rule ReClassesHaveNoReferencesCondition

[hernanmd]

Bug description
It seems we have a problem with the rule ignoring classes not referenced, specifically the method: ruleClassNotReferencedRuleV1FalsePositive. When you mark a class reference as false positive, for instance, MyClassNonEmptyLeafUnused, that method is populated with an entry and we get something like this:

ruleClassNotReferencedRuleV1FalsePositive

	<ignoreForCoverage>
	^ #(#(#(#RGClassDefinition #(#RBHierarchySubclassBForClassVariable)) #'2024-07-18T12:39:47.723158+02:00') #(#(#RGClassDefinition #(#MyClassNonEmptyLeafUnused)) #'2024-07-18T12:40:19.70241+02:00') #(#(#RGClassDefinition #(#RBDummyCompositeLintRuleTest)) #'2024-07-18T12:40:19.702201+02:00') #(#(#RGClassDefinition #(#RBClassUsingSharedPoolForTestData)) #'2024-07-18T12:40:19.701335+02:00') #(#(#RGClassDefinition #(#RBBasicDummyLintRuleTest)) #'2024-07-18T12:40:19.702472+02:00') #(#(#RGClassDefinition #(#RBTransformationRuleTestData2)) #'2024-07-18T12:40:19.701755+02:00') )

We could remove, of course, the introduced class ManifestRefactoringDataForTesting. But we would get back all the same errors we were getting without the Manifest.

What I will do is update the ReClassesHaveNoReferencesCondition>>violators method to discard those classes that are manifest. That would require implementing isManifest in RB-related classes.

To Reproduce
See PR #16917