dev: lets ConstructingMemberAssertionTestCases consider only class

types, not interface types.
dev: lets GuardClauseAssertionTestCases consider only class

types, not interface types.
dev: lets TypeMembers don't ignore inteface members.
docs: adds release note for test cases to consider only class types

rather than interface types.
refactor: improves test assertions.
dev: deletes the unused ConstantEqualityComparer class.
dev: renames SpecimenBuilderAdapter to SpecimenBuilder.
dev: renames BaseTheoremAttribute to TheoremBaseAttribute.
dev: renames BaseFirstClassTheoremAttribute to

FirstClassTheoremBaseAttribute.
style: reformats code in TypeMembers.
dev: renames AccessibilityCollectingVisitor to AccessibilityCollector.
dev: renames ReferenceCollectingVisitor to ReferenceCollector.
dev: renames ElementReferenceCollectingVisitor to ElementReferenceCollector.
dev: introduces the MemberKinds enumeration.
dev: implements MemberKindsCollector.
dev: deletes unnecessary method implementions of

AccessibilityCollector.
dev: implements the IdiomaticMembers class.
dev: introduces the IIdiomaticMemberAssertion interface.
build: addresses some code-analysis warnings.
dev: implements GetIdiomaticMembers method.