$ref does not consider schema resources in v2019-09

[Whathecode]

trafficstars

Schema resources are schema documents included in compound schema documents.

Each schema with an $id in a Compound Schema Document is called a Schema Resource.

Several tests for v2019-09 are currently failing because these schema resources are not considered while resolving $ref.

For example, the second and third test in V2019JsonSchemaTest.testAnchorValidator() fails since http://localhost:1234/bar and http://localhost:1234/nested.json is not retrieved through the schema resource, but is attempted to be retrieved through normal URI retrieval.

Sidenote: the first test case in that unit test is fixed considering this open PR that makes $anchor work. I'm opening this bug report since it's not specific to anchor.

Another example is V2019JsonSchemaTest.testRefValidator(). This fails since http://localhost:1234/tree can't be retrieved.

[Whathecode]

Note that I already managed to make the second test of V2019JsonSchemaTest.testAnchorValidator() and all of testRefValidator() pass by the changes described in the PR. But, this wasn't exactly production-ready code so didn't commit it.

While playing around (not committed), I did manage to make the second "$ref": "http://localhost:1234/bar#foo" test pass, by doing a recursive lookup of all containing JsonNodes with $id set and storing it in ValidationContext. This was then retrieved in RefValidator.getRefSchema(). However, this fails for the last test which has a nested non-absolute "$id": "nested.json". Trying to resolve that as a full id was resulting in stack overflows, etc., and made me reach the limit of how much time I want to invest in this, so I won't add anything else to this PR.

It may offer a first suggested approach on how to tackle this.