feat: Add Draft 2020-12

[Roman3349]

Description

Adds basic support for Draft 2020-12, based on the Draft 2019-09 implementation. Only changes required by the 2020-12 specification are made. The motivation was to add the draft 2020-12 to validate the OpenAPI specification v3.1, which is a subset of the draft 2020-12.

• New Draft2020 constraint set (copied from Draft2019) and a draft2020-12 dialect registered in Factory.
• prefixItems/items as required by 2020-12:
  • additionalItems is removed and the array form of items is replaced by prefixItems.
  • New PrefixItemsConstraint validates array items by position.
  • items now takes a single schema and only applies to items after those covered by prefixItems.
• Bundled, flattened meta-schema dist/schema/json-schema-draft-2020-12.json, plus its URL mapping in UriRetriever.
• format is an annotation by default, as 2020-12 requires (§7.2.1: assertion "MUST be disabled by default"). The new Constraint::CHECK_MODE_FORMAT_ASSERTION flag enables it. CHECK_MODE_DISABLE_FORMAT wins if both flags are set. Other drafts are not affected.
• The JSON Schema Test Suite now runs for draft2020-12 in strict mode. The optional/format tests run with CHECK_MODE_FORMAT_ASSERTION enabled.

Same limitations as Draft 2019-09, and the matching test cases are skipped:

• $dynamicRef/$dynamicAnchor are not supported (the successors of $recursiveRef/$recursiveAnchor, which aren't supported in 2019-09 either).
• unevaluatedItems/unevaluatedProperties are not supported.
• $vocabulary is not supported (optional/format-assertion.json).
• The optional test cases skipped for 2019-09 (ECMAScript regex, bignum, some formats, …) are skipped for 2020-12 as well.

Related Issue

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code refactoring
• Other (please describe):

Checklist

• I have read the CONTRIBUTING guidelines
• My code follows the code style of this project
• I have added tests that prove my fix is effective or that my feature works
• All new and existing tests pass
• I have updated the documentation accordingly
• My changes generate no new warnings

Additional Notes