[META] Approachable Runtime Field Creation

[elastic-jb]

We now have the primary experience for Runtime Fields in the product, but we can do a lot to make it easier for existing users and more friendly to users who are new to the Painless language. These items are experiences and improvements targeted at increasing the adoption by making the authoring experience more approachable.

• Preview experience for Runtime Fields that output a single script (7.15)
• Improve online Painless documentation
• [Runtime Fields] UX: Editor in-product documentation consistent with new Lens formula function documentation #105521
• Type-specific helper text for Runtime Field Editor, no more "blank box"
• User experience for creating Runtime Fields for common use cases from field list
• Script Templates for common intermediate use cases like logic, iterating or complex parsing
• UX for selecting fields, functions similar to Drilldown tokens

If you have other suggestions that we should consider or know of other issues that are relevant to this workstream, please link or comment on this issue.

[elasticmachine]

Pinging @elastic/kibana-app-services (Team:AppServices)

[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.