Feature: Entity Item Ref Extension

[madsrasmussen]

This PR introduces a new extension point and a new element to render the extension "Entity Item Ref."

The extension point is used to render a list of references based on the "Item" model. The extension point will be used in pickers and reference lists where we, in some cases, can get a list of different entity types and therefore cannot hardcode the rendering of the list.

The item ref makes a lookup in the extension registry based on the "entity type" on the model and finds a matching extension. It is thereby possible to use a rendering specific to the type. If no matching extension can be found, it will use a default rendering.

The many changes is this PR is also caused be some item repositories/types being moved around

Here are some key areas to look at:

• The new extension type including element: https://github.com/umbraco/Umbraco-CMS/tree/v15/feature/entity-item-ref-extension/src/Umbraco.Web.UI.Client/src/packages/core/entity/entity-item-ref
• Implementation for document: https://github.com/umbraco/Umbraco-CMS/tree/v15/feature/entity-item-ref-extension/src/Umbraco.Web.UI.Client/src/packages/documents/documents/item
• Implementation for member: https://github.com/umbraco/Umbraco-CMS/tree/v15/feature/entity-item-ref-extension/src/Umbraco.Web.UI.Client/src/packages/members/member/item
• Implementation for user: https://github.com/umbraco/Umbraco-CMS/tree/v15/feature/entity-item-ref-extension/src/Umbraco.Web.UI.Client/src/packages/user/user/item

Manifest:

{
  type: 'entityItemRef',
  alias: 'Umb.EntityItemRef.Document',
  name: 'Document Entity Item Reference',
  element: () => import('./document-item-ref.element.js'),
  forEntityTypes: [UMB_DOCUMENT_ENTITY_TYPE],
},

Using the element:

<uui-ref-list>
  <umb-entity-item-ref .item=${itemGoesHere}>

    <uui-action-bar slot="actions">
      <!-- actions goes here -->
    </uui-action-bar>

  </umb-entity-item-ref>
</uui-ref-list>

The PR implements the new umb-entity-item-ref element for three pickers as a test:

• Document
• Member
• User

In addition, I have also aligned the UX of the pickers so they all support opening the workspace from the item and respect the section permissions.

What to test:
Please ensure that the pickers mentioned above work as expected.