[WIP] Make Schema type retrieval and checks 3.1 compatible

[g-getsov]

Swagger Parser only populates the Schema's type field for OAS 3.0.X and under. For schemas versioned 3.1.0 and above the type will be populated in the types field instead (reference).

The solution proposed by swagger-parser is to set the System property bind-type which will ensure that the getType() method of the Schema object will perform the same process of extracting the type as the ModelUtils.getSchemaType() function that I've implemented in this MR.

I believe that using the proposed ModelUtils.getSchemaType() function will allow for more flexibility when writing logic for backward compatibility that might require a distinction of the origin of the type field.

This MR makes almost all type checks spec version agnostic which should hopefully resolve a good chunk of edge cases for 3.1.0 generations.

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[wing328]

@g-getsov thanks for the PR. Can you please PM me via Slack to discuss this PR when you've time next week?

https://join.slack.com/t/openapi-generator/shared_invite/zt-12jxxd7p2-XUeQM~4pzsU9x~eGLQqX2g

[wing328]

@g-getsov fyi I've merged https://github.com/OpenAPITools/openapi-generator/pull/18313 to better handle array schema in 3.1 spec