Upgrade to Jackson 3

[filiphr]

• Change imports for com.fasterxml.jackson.databind and com.fasterxml.jackson.core to tools.jackson.databind and tools.jackson.core
• Upgrade com.networknt:json-schema-validator to 3.0.0 (Jackson 3 support)
• Adjust Jackson 2 iterators to Jackson 3 collections
• Use non-deprecated isString / asString / stringValue instead of isTextual / asText / textValue
• Use StringNode instead of TextNode
• Use JsonMapper#shared instead of underlying Schema Config ObjectMapper in SubtypeResolutionSimpleIntegrationTest since schema validation requires numbers, but underlying Object Mapper uses strings for numbers

This is for #553

[filiphr]

The change here is due to FasterXML/jackson-databind#5417. Looking at the code I assume that if the array node contained null the method would return null as well. In Jackson 3 using arrayItem.asText(null) with a NullNode is going to return the empty string. Therefore, we do a check on isNull instead of using asText(null)

[filiphr]

I had to change this to use JsonMapper.shared(), because the object mapper from the config has JsonWriteFeature.WRITE_NUMBERS_AS_STRINGS. This leads to generating

{
  "supertypeA" : {
    "@type" : "SubClassA",
    "aProperty" : "a"
  },
  "supertypeB" : {
    "@type" : "SubClassB",
    "bProperty" : "98"
  }
}

In the schema for TestSubClassB the bProperty is expected to be integer.

For some reason with Jackson 2 and the way the default ObjectMapper is created the generated JSON is

{
  "supertypeA" : {
    "@type" : "SubClassA",
    "aProperty" : "a"
  },
  "supertypeB" : {
    "@type" : "SubClassB",
    "bProperty" : 98
  }
}

[filiphr]

I didn't realize that the project is Java 8 baseline. As part of this commit I also upgraded the baseline to Java 17. If it is preferred, I can do that as part of a separate PR

[CarstenWickner]

Thanks @filiphr for doing the heavy lifting here.
Since the various tests appear to be successful, I'm confident you've covered all important aspects.

I'll try to get Java 21 as a secondary branch build environment up and running, now that Java 11 is no longer in the mix.

[filiphr]

Thanks a lot @CarstenWickner. I was happy to help.

I also wanted to do another PR updating to the latest GitHub Actions and also do Java 21. BTW, there would be some failures on Java 21 I think, BigDecimal has a field named hash now, so one of the tests would fail

[CarstenWickner]

Hi @filiphr

That'd be greatly appreciated. Assuming you have some experience with the latest GitHub Actions, I'd gladly leave that to you.
I'm currently just updating various other dependencies (to make use of the major version upgrade).