Add support for JTD (JSON Type Definitions)

Is your enhancement related to a problem? Please describe.

Seeing that eg. ajv has started to support JTD (even with some JTD-exclusive features and that JTD itself is published as a final (although experimental) RFC 8927 (unlike JSON Schema which is stuck in an eternal stream of drafts) + seeing how JTD covers a simplified, and strictly type related, subset of what JSON Schema covers, making it more of a 1:1 match with the type systems of eg. TypeScript – that makes it rather appealing to be able to get schema support for JTD-schemas in addition to the current support for JSON Schemas.

Describe the solution you would like

The addition of support for JSON Type Definitions, JTD:s, schemas alongside JSON Schemas.

Describe alternatives you have considered

Alternative would be for those who use JTD:s to eg. convert them to JSON Schema when they want this plugin to make use of them, or to write both JTD:s and JSON Schemas, with the risk of the two diverging and giving different validation results for the same input.

Additional context

There exists multiple implementations and tools for JTD at https://jsontypedef.com/docs/implementations/

The issue points to the existing JSON Schema support as the starting area, but names no files, tests, or entry points. First map how that support is exposed in vscode-yaml; done means JTD schemas work alongside JSON Schemas without requiring conversion.