Unexpected properties in ComponentSource data

Problem/Motivation

While working on #3574548: Unexpected properties in ComponentSource data, we noticed some unexpected node_id and third_party_settings values (always empty, of course, they don't make sense here) added to ComponentSource data:

node_id: 699714c9b5736
source_id: component
source:
  component:
    component_id: 'ui_suite_daisyui:avatar'
    variant_id: {}
    props: {}
    slots: {}
    third_party_settings: ''
    node_id: ''

They may come from ComponentForm:

  public static function valueCallback(&$element, $input, FormStateInterface $form_state) {
    if ($input) {
      $value = [
        'component_id' => $input['component_id'] ?? NULL,
        'variant_id' => $input['variant_id'] ?? NULL,
        'props' => $input['props'] ?? [],
        'slots' => $input['slots'] ?? [],
        'third_party_settings' => $input['third_party_settings'] ?? NULL,
        'node_id' => $input['node_id'] ?? NULL,
      ];
      $element['#default_value'] = $value;
      return $value;
    }
    else {
      return [
        'component_id' => NULL,
        'variant_id' => NULL,
        'props' => [],
        'slots' => [],
        'third_party_settings' => NULL,
        'node_id' => NULL,
      ];
    }
  }

Introduced in #3551360: Add third party settings and tree Node ID in field storage.

Proposal

A naive solution would be to move third_party_settings and node_id at the same level than source_id and source for SDC components:

node_id: 699714c9b5736
source_id: component
source:
  component:
    component_id: 'ui_suite_daisyui:avatar'
    variant_id: {}
    props: {}
    slots: {}
third_party_settings: {]

But those properties are expected there for any source plugin targeting slots (BlockSource, WysiwygSource...), so it may be better to manage it in a more generic way. I am not opposing to implement it for all sources, even the ones not targeting slots, if it is the cleanest way to do it, because we never know, it may be useful later.