[java][jersey2-client] Disable coercion of scalars

Created by: bkabrda

I have a schema that has a oneOf with two choices, one is an alias for string and the other for int:

components:
  schemas:
    Something:
      type: object
      oneOf:
        - $ref: '#/components/schemas/One'
        - $ref: '#/components/schemas/Two'
    One:
      type: string
    Two:
      type: integer

The problem is that when the API returns a string that has integer in it, e.g. "1234", the Jackson library (which has coercion of scalars turned on by default) fails to deserialize the Something object, as "1234" deserializes successfully as both Integer and String. This PR disables scalar coercion to prevent this, thus making the above example work. (As an additional note, I think we want to have this feature disabled since it is something that other clients don't do)

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