Adds requiredVarsMap

[spacether]

Adds requiredVarsMap to store required variable names whether or not they have a defining schema
When merged this will close out #8906

• Uses it in python-experimental
• Turns on 3.0.3 unit tests that were excluded by [BUG] Core java schema classes missing schema required property names + requiredVars values #8906

This will allow our java schema classes to accurately keep track of when variables are required.
Use cases for requiredVarsMap are:

1. required property is defined in properties, value is that CodegenProperty
2. required property is not defined in properties, and additionalProperties is true or unset value is CodegenProperty made from empty schema
3. required property is not defined in properties, and additionalProperties is schema, value is CodegenProperty made from schema
4. required property is not defined in properties, and additionalProperties is false, value is null

This will allow our generators to do two things:

1. list out the required property names by using the keys from that map
2. create type hints where one can, by using the CodegenProperty value from the map. For example this could be used on instantiation input signatures.

requireVars note

Long term this can replace requiredVars which only knew about use case 1 and did not include use cases 2-4.

TODO for the future

one will need to be able to detect if the schema for a required property

• does not exist because additionalProperties = false (use case 4)
• is AnyType because additionalProperties is unset (use case 2)
• is AnyType because additionalProperties is true or empty schema (use case 2)
• is a specific schema/property because additionalProperties is set or the property is set (use case 1 + 3)

Note: for evaluation of additionalProperties unset, unevaluatedProperties will need to not include annotations from unset additionalProperties so omitting that additionalProperties from definitions would help add that feature in the future.
To detect that:

• additionalProperties will need to have the value of null when it is unset, AND
• one could keep the True/False values if one wanted, or one could keep writing AnyType/NoType schemas rather than the booleans.
• The more general case is to accept True/False/Schema but not many generators could accept that.

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