Add support for field widget actions

Issue information

From user: jurgenhaas

Contribution record

Fork management

Problem/Motivation

Based on #3528684: Add processor and field widget assist plugin system to AI Content Suggestions there is now a field widget action where we can build plugins that provide a widget next to form fields where the plugin takes some input from the form, runs through some processes and returns results back to the form.

Proposed resolution

Let's provide ECA integration for that.