Test relative JSON Pointer index manipulation

[dev-willbird1936]

Summary

• add valid Relative JSON Pointer format cases for forward, backward, and zero index manipulation;
• add malformed index-manipulation controls; and
• cover both Draft 2020-12 and the future v1 draft while leaving older drafts unchanged.

Why

Draft 2020-12 added the optional +N / -N index-manipulation production, but the shared format suite did not exercise it. These cases provide implementation-neutral coverage and are a prerequisite for python-jsonschema/jsonschema#1534.

Specification: https://json-schema.org/draft/2020-12/relative-json-pointer

Validation

• python -m json.tool for both changed files
• python bin/jsonschema_suite check — 11 checks passed, 4 skipped
• git diff --check

[jdesrosiers]

We've recently completed a major update to format validation as part of a Google Summer of Code project. Several tests were added already. Please review the recent changes. If those are enough, great! Otherwise, please rebase your branch and include any tests you think are still missing. Sorry of the delay.

[jdesrosiers]

@dev-willbird1936 These tests will need to be added to draft7 and draft2019-09 as well.

@vtushar06 Would you mind reviewing this? I'm guessing you might be more familiar with the spec than me at the moment.