Problem/Motivation
To get around all the UX issues identified in #3431164: [meta] Improve the "Expose all fields as blocks to Layout Builder" feature with this configuration page, we can instead use a Feature Flag #3423352: Add an API for feature flags
This configuration is essentially being used as a feature flag currently, but does not need to be. The behaviour when this configuration is enabled is only there for BC purposes, it is not recommended for new sites to enable it. Therefore, we shouldn't be using configuration as this will lead to issues in the future when we need/want to deprecate/remove this behaviour.
Feature flags allow us to do this gracefully, and get around all of the issues with exposing this behaviour via configuration.
Proposed resolution
Remove configuration and form
Remove settings form tests
Swap configuration check with a moduleExists
Remaining tasks
User interface changes
Remove Layout builder Settings form.
API changes
None
Data model changes
None
Release notes snippet
N/A
