Create new Templates menu

Edited the issue summary to note that only content types (node bundles) are in scope at this stage.

hooroomoo → changed the visibility of the branch 3541027-create-new-templates to hidden.

The blocker 📌 Create HTTP Endpoint for View modes/content templates Active just landed! 🤝

MR #1 is 3541027-create-new-templates. It is not in a merge-able state. I added a bunch of todos it still needs. But it should be enough to get started on MR #2.

I was able to create a Content Template without the Add new template button by importing config. Leaving it at the bottom of the comment in case its useful.

/admin/config/development/configuration/single/import

uuid: 963372a4-3ebb-46c9-8ae5-e3a27b5e5e97
langcode: en
status: false
dependencies:
  config:
    - canvas.component.sdc.canvas_test_sdc.my-cta
    - core.entity_view_mode.node.full
id: node.article.full
content_entity_type_id: node
content_entity_type_bundle: article
content_entity_type_view_mode: full
component_tree:
  -
    uuid: 435d1d20-a697-4d36-9892-9d61c825c99c
    component_id: sdc.canvas_test_sdc.my-cta
    component_version: 53ed322c96bee384
    inputs: '{"text":"This is really tricky for a first-timer","href":{"sourceType":"static:field_item:uri","value":"https:\/\/drupal.org","expression":"\u2139\ufe0euri\u241fvalue"}}'
    label: yo
exposed_slots: {  }

MR 1 is committed, MR 2 is in progress, the add template dialog works but needs some loading spinners for the view modes request, and the form isn't quite what I'd expect if I choose a content type that already has a template assigned to the "full" view mode.

It should be jump-onable by folks in other timezones - it all works and the TypeScript is sorted out, but needs some refining. The dialog props were set up knowing it will evenually be opened by a bundle's contextual menus, too.

Regarding the "Add new template" modal (MR #2), product/design said to keep the wording the screenshot as is. So use "Template" and "Existing templates" instead of "view mode". I updated the issue summary.