[Core] Added members for circular refs and container of models

Created by: AIexG

Added a member circularReferences to CodegenModel which stores all circular referenced schemas. Created ModelUtils method getCircularReferencedSchemaNames() to call recursive detectCircularReferences() to store all found circular references in a Set of strings. Set gets stored in circularReferences.

Add a member flag to CodegenProperty which is true if an array schema consists of object schema items.

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Related feature request

closes #4757

Additional context

First pull request(s), hopefully doing everything right!

technical committee

cc @OpenAPITools/generator-core-team