feat: make getMatchingSchemas return keys matching propertyNames schema

[marcopiii]

Despite the possibility to validate a key against a schema using propertyNames, LanguageService.getMatchingSchemas doesn't return such matches.

This little change fixes that and would solve #89

Example

Given a schema like this

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "definitions": {
    "id": { "type": "string", "my-custom-metadata": "foo" },
  },
  "type": "object",
  "properties": {
    "name": { "type": "string" },
    "things": {
      "type": "object",
      "propertyNames": { "$ref": "#/definitions/id" },
      "additionalProperties": { "type": "string" }
    }
  }
}

a json like this

{
    "name": "Tony",
    "things": {
        "f2617076": "hat",
        "2ae481ea": "skateboard"
    }
}

would produce the following matches

[
  ...,
  {
    node: StringASTNodeImpl {
      offset: 46,
      length: 10,
      type: 'string',
      value: 'f2617076'
    },
    schema: { type: 'string', 'my-custom-metadata': 'foo' }
  },
  {
    node: StringASTNodeImpl {
      offset: 73,
      length: 10,
      type: 'string',
      value: '2ae481ea'
    },
    schema: { type: 'string', 'my-custom-metadata': 'foo' }
  },
  ...
]

[aeschli]

Can you add tests?

[marcopiii]

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[marcopiii]

Can you add tests?

@aeschli i hope i did the right thing with the test, let me know if anything else is needed 👍