Feat adds has discriminator with non empty mapping

[spacether]

Adds hasDiscriminatorWithNonEmptyMapping
This template variable can be used to tell if there is or isn't a discriminator that needs to be defined.
This variable is needed in addition to the discriminator one because in by python-experimental branch, the discriminator has an indent applied to it. That indentation makes it impossible to generate code to check discriminator presence at the right indentation level (at the model level).
We need a schema level boolean variable that says the discriminator exists or not and this is it.

This variable can be used to determine if a custom schema or model needs to be written for an object schema.
A custom object schema model will need to be made if any of these conditions are met

• hasVars
• hasValidation
• isNullable
• hasRequiredVars
• additionalPropertiesIsAnyType is False
• hasDiscriminatorWithNonEmptyMapping

This will be used to generate DictSchemas only when needed in #8325

discriminators are only supported in request bodies and response payloads per OpenApi
But this interface is needed on all Java classes that implement Schema to allow robust generation by templates.
So it's needed in:

• CodegenModel
• CodegenProperty
• CodegenParameter
• CodegenResponse

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[spacether]

The error is unrelated to this PR