Support nested autocomplete attributes

Problem/Motivation

If you try to configure a nested autocomplete attribute (eg body.value), the json response will be unkeyed. Therefore autocompletes using this will not return any values.

>>> $jc->search('node--article', 'body.value', 'two');
PHP Warning:  Undefined property: stdClass::$body.value in /var/www/html/web/modules/contrib/jsonapi_reference/src/JsonApiClient.php on line 118
 [error]  JSON:API entrypoint https://d10.ddev.site/jsonapi returned no data for path https://d10.ddev.site/jsonapi/node/article when searching for objects where the body.value attribute matched "two".
=> [
     "" => "34c70d67-610c-49b3-8b9b-c6e2bc51e80a",
   ]

Whereas for simple attributes, eg title, this works:

>>> $jc->search('node--article', 'title', '2');
 [error]  JSON:API entrypoint https://d10.ddev.site/jsonapi returned no data for path https://d10.ddev.site/jsonapi/node/article when searching for objects where the title attribute matched "2".
=> [
     2 => "34c70d67-610c-49b3-8b9b-c6e2bc51e80a",
   ]

Steps to reproduce

See drush example above.
Or create a typed resource object field that uses a nested autocomplete attribute (eg body.value) and watch it fail to ever match any content.

Proposed resolution

TBD

Remaining tasks

All the things.

User interface changes

Probably none.

API changes

Probably none.

Data model changes

None.