Introduce format-assertion 2020-12 and 2019-09 dialects

[jviotti]

Signed-off-by: Juan Cruz Viotti jv@jviotti.com

[augmentcode]

🤖 Augment PR Summary

Summary: This PR introduces “format-assertion” dialect meta-schemas for JSON Schema 2019-09 and 2020-12.

Changes:

• Added README entries linking to the JSON Schema 2019-09 and 2020-12 specifications
• Added a 2019-09 dialect meta-schema intended to treat format as an assertion
• Added a 2020-12 dialect meta-schema that enables the official format-assertion vocabulary
• Added test fixtures for both dialect meta-schemas to validate accepted/rejected schema shapes

Technical Notes: The new dialect files are expressed as JSON Schema resources with $vocabulary declarations and delegate structural validation via $ref to the corresponding upstream draft meta-schemas.

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[augmentcode]

schemas/2020-12/ietf/jsonschema/2019-09/dialect/format-assertion.json:8: This dialect is described as making format an assertion, but the 2019-09 https://json-schema.org/draft/2019-09/vocab/format vocabulary defines format as an annotation (the true/false here only indicates required vs optional vocabulary support). As written, this dialect mainly flips the official 2019-09 meta-schema’s format vocabulary from false to true, which may not actually provide “assertion” semantics to consumers.

Severity: medium

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