[Bug] Backward compatibility check fails on reordered discriminator mappings

[OllieKosh]

Ran into a compatibility issue, which I believe is a false positive. I have one polymorphic schema, that maps to two different property names. The backwards compatibility check fails if the mappings are re-ordered.

This should not be failing, because neither discriminator names nor the mapping changed.

For example, the following 2 should be considered compatible, but are not. Assume the actual schemas are identical. Schema A is mapped to a-type and z-type which are present in both mappings, but are ordered differently.

             schema:
               oneOf:
                 - $ref: '#/components/schemas/A'
                 - $ref: '#/components/schemas/B'
               discriminator:
                 propertyName: realtype
                 mapping:
                   z-type: '#/components/schemas/A'
                   a-type: '#/components/schemas/A'
                   b-type: '#/components/schemas/B'

and

              schema:
                oneOf:
                  - $ref: '#/components/schemas/A'
                  - $ref: '#/components/schemas/B'
                discriminator:
                  propertyName: realtype
                  mapping:
                    a-type: '#/components/schemas/A'
                    z-type: '#/components/schemas/A'
                    b-type: '#/components/schemas/B'

I was able to reproduce this in this repo by adding a test to OneOfDiffTest with the above as an example (based on oneOf_discriminator-missing_1.yaml).

  @Test
  public void testOneOfDiscrimitatorDifferentOrder() {
    assertOpenApiAreEquals(OPENAPI_DOC11, OPENAPI_DOC12);
  }