Hack around limitation that prevents $ref: ...s from having siblings

[gnidan]

For any schema that defines a $ref property alongside any other properties, docusaurus-json-schema-plugin currently loses all other properties and treats the schema as just the $ref'd other schema itself. This is because docusaurus-json-schema-plugin uses the now-unmaintained @stoplight/json-ref-resolver, which is stuck on the old JSON Schema drafts 4-7 semantics. (In those older drafts, this behavior was correct.)

To work around this issue:

• Expand the existing schema preprocessing logic to detect all $ref's with siblings

• For each such case, replace the { $ref: "...", ...props } with that $ref moved into an available schema composition keyword. (e.g., it might become { ...props, allOf: [{ $ref: "..." }] }).

• Throw an error if the schema uses all three composition keywords and there's no place for this weird unnecessary composition. (This seems quite unlikely, though)

• Override docusaurus-json-schema-plugin's rendering to detect this preprocessed "unnecessary composition" and treat it as a special-case apart from the normal way it presents lists of composed schemas.

• When a schema composition is used with only one item, treat it as representing the extension of a base schema, and present it as such.

• Present purely annotative extensions with less visual clutter (like, for when a schema is just { $ref: "...", description: "..." }