[Discover] Enable field examples for _score field in the sidebar field popover

[jughosta]

In the new <FieldStats /> component we show "Analysis is not available for this field." for _score field. Although we used to have stats before:

We could improve it by fetching 100 examples of _score field if:

• we skip exist filter for it src/plugins/unified_field_list/common/utils/field_stats_utils.ts (buildSearchParams)
• we add sort to the request (see [Discover] Pass current sort order to fetch more relevant examples in FieldStats for nonaggregatable fields #140732)
• and we enable fetching for _score in src/plugins/unified_field_list/common/utils/field_examples_calculator.ts (canProvideExamplesForField)

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)

[kertal]

Closing this because it's not planned to be resolved in the foreseeable future. It will be tracked in our Icebox and will be re-opened if our priorities change. Feel free to re-open if you think it should be melted sooner.