feat: refactor to use diagnostics providers

[srivastava-diya]

Description

This PR adds JSON schema validation using @hyperjump/json-schema and @hyperjump/json-schema-errors

Changes

1. In SyntaxValidation.ts : Extracted the syntax diagnostic logic from JsonValidation.ts into a standalone function getSyntaxDiagnostics(textDocument, parseErrors): Diagnostic[]. No server, no connection just input and output.

2. In SchemaValidation.ts : A standalone function getSchemaDiagnostics(textDocument, tree, schemaUri, documentMap) that handles schema validation. It reads the $schema field from the document, parses the JSON, runs it through @hyperjump/json-schema's validate() with BASIC output format, and maps errors back to document ranges . Also contains MatchingSchemaCollector , an EvaluationPlugin that hooks into evaluation lifecycle via afterKeyword to collect per-instance-location schema matches. Not used for validation itself, but will power future features like hover tooltips and completions.

3. In JsonValidation.ts : it acts as the orchestrator now. Calls both getSyntaxDiagnostics and getSchemaDiagnostics, and sends a single combined sendDiagnostics call thus prevents overwriting.

4. Integrated @hyperjump/json-schema-errors for better error messages. Added a formatError helper that recursively formats nested anyOf/oneOf alternatives with indentation.

5. Tests added: valid case, invalid case with message content assertions, and anyOf and OneOf formatting case.

Screenshots