Continue to output configured fields when layout builder is activated

When a custom-element display config is configured to output with layout builder, the module continues to output fields, that are configured next to the layout builder, now.

If display config has fields configured next to enable layout builder, the output is/was:

Before (3.0.x):

{
    "element": "node-page",
    "sections": [
        {
            "element": "drupal-layout",
            "layout": "layout_onecol",
            "content": [...]
        }
    ]
}

After (>=3.1.0):

{
    "element": "node-page",
    "created": "1736421462",
    "title": "My custom page",
    "body": "<p>The is my content</p>",
    "sections": [
        {
            "element": "drupal-layout",
            "layout": "layout_onecol",
            "content": [...]
        }
    ]
}

If the new behavior is unwanted, simply make sure that unwanted fields are removed from the configuration.

Updating

For existing sites the fields are automatically removed from the configuration, so the output does not automatically change with the update. Given that configuration, the variant of 3.0.x is still output with >3.1.x
Still, for future configuration, watch out to add the fields only when actually desired.