Provide an option to remove entity reference field item content wrappers for Rendered entity field formatter.

Problem/Motivation

When rendering entity reference field items (node, taxonomy_term, ...) it is impossible to override the view mode templates (node--teaser.html.twig, ...), meaning, although field wrappers can be controlled from the module, it does not provide sufficient markup control when rendering entities from entity reference field to fully remove HTML wrappers when rendering referenced field item content.

Steps to reproduce

Add an entity reference field to Manage Display and set the field Format to the Rendered entity. If rendered entity uses the twig template for the selected display mode (e.g., node--teaser.html.twig, ...) the template can add undesired wrapping markup.

Proposed resolution

Provide an option to remove item content wrappers when rendering entity reference filed item content, i.e., loop through field items, check for and override content #theme with no-wrappers template provided by fences module.

Remaining tasks

Review and community test the merge request.

User interface changes

Add Override Referenced Field Item Content Template Theme checkbox to Entity Reference type fields.

Data model changes

Update configuration schema.