Boolean scripted fields aren't handled correctly in the filter bar

[Bargs]

Kibana version: master
Elasticsearch version: master

Describe the bug:

When creating a filter on a boolean scripted field matching the value false the filter pill displays the full script instead of a human readable display name.

The problem is that we're returning params.value here which incorrectly tells the phrase mapper that this is not a scripted field. At the moment I'm not sure why we're returning params.value so we need to look into that a bit before we'll know what the appropriate fix is.

Steps to reproduce:

1. Create a boolean scripted field
2. Create a filter on it for the value false using the Add Filter UI
3. Notice the text in the filter pill that gets created

Screenshots (if relevant):

[elasticmachine]

Pinging @elastic/kibana-app

[elasticmachine]

Pinging @elastic/kibana-app-arch (Team:AppArch)

[lukasolson]

Still an issue, though the behavior now doesn't show the whole scripted field, it shows basically nothing:

[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.