Consider also adding "propertyNames" to getMatchingSchemas

I don't know if this was intentional or not, but schemas matching "propertyNames" are not added to matchingSchemas.

See https://github.com/microsoft/vscode-json-languageservice/blob/main/src/parser/jsonParser.ts#L946

For the extension I'm developing it would be nice to have propertyNames also included in matchingSchemas.

In my testing so far it seems fine to include propertyNames into matchingSchemas.

To explain my use case a bit more:

imagein you have the following json

{
  "definitions": {
    "foo": 1,
    "bar": 2
  },
  "reference": "foo"
}

I want to validate that the value of reference is consistent with the keys in definitions. So allowed values would be "foo" and "bar". This is obviously not possible with JsonSchema alone.

It would work if we would collect propertyNames in matchingSchemas and then iterate over matchingSchemas to find the properties and see if they are consistent with the reference.

Start in src/parser/jsonParser.ts around line 946, where schemas are added to matchingSchemas, and trace how propertyNames is handled. Include propertyNames in matchingSchemas and verify that the collected schemas support the described property-name use case.