Fixes issue 1975: bug in const processing, const values of all types now processable

[spacether]

Changes const type from String to Object Per json schema docs, const stores one values of any json schema type

• json schema spec const definition
• understanding const docs
• real world examples of const values in the json schema test suite, the schema value stored in the "schema" key: https://github.com/json-schema-org/JSON-Schema-Test-Suite/blob/main/tests/draft2020-12/const.json#L6

Verification:

• java tests added verifying ingestion of json null/string/number/object/array/boolean

If merged, this will close out these issues:

• https://github.com/swagger-api/swagger-parser/issues/1975
• https://github.com/swagger-api/swagger-parser/issues/1966

[spacether]

@frantuma @gracekarina thank you for your work on swagger-parser. When you have some time can you review this PR? How do I get CI tests to run? The test that I added passes locally. Getting this merged in and released would help me turn on 34 json schema tests in openapi-json-schema-generator Thank you!

[frantuma]

Thanks!

[spacether]

Thanks you for the review and merge!