Scaffold components config array instead of string

Problem/Motivation

Following #3615841: Config exclude_id array instead of string, the Scaffold panel's components setting is still stored as a single string with line breaks:

  scaffold:
    components: "ui_suite_bootstrap:grid_row\r\nui_suite_bootstrap:grid_row_1\r\nui_suite_bootstrap:grid_row_2"

ScaffoldPanel splits it again on every render.

IslandConfigurationFormTrait only converts exclude_id, by key name, so every new list setting needs another hardcoded key.

The component_status checkboxes keep unchecked values, so profiles store deprecated: '0' and obsolete: '0'.

Proposed resolution

• Store scaffold.components as a list. It is still edited in a textarea, one id by line.
• IslandConfigurationFormTrait::submitConfigurationForm() turns a submitted string into a list when the island's default value for that key is an array. No key names are hardcoded, and this also covers exclude_id.
• The trait drops unchecked component_status values, as it already does for exclude.
• Add the post update display_builder_post_update_scaffold_components_as_list() to convert stored profiles.

Remaining tasks

• Review

User interface changes

None.

API changes

IslandConfigurationFormTrait: in a contrib island using the trait, a submitted string for a key whose default value is an array is now stored as a list.

Data model changes

display_builder.islands.scaffold.components changes from string to a sequence of strings. A post update converts existing profiles.