Allow working with a new (unsaved) entity

Or … better yet: what if we allow navigating to /xb without any entity, which then would load the XB UI without any request to /xb/api/v0/layout/{entity_type}/{entity}.

I'll get a draft MR going with the server-side bits.

Quickly hacked together an initial MR, seems to at least kinda work? Now just needs JS updates to finish booting :)

Oh and this of course would still show the navigation bar with the UI:

Created 📌 Add permission for "Use Experience Builder" Active , and postponed on this

Just discussed this with @effulgentsia and @penyaskito. We agreed that create access for the xb_page content entity type would be a reasonable first step until 📌 Allow XB to be used on all node types Active happens.

This blocks:

• ✨ Move entity type and ID from base path and into routing parameters Active
• 📌 Add generic create entity support Active

I don't think this needs to block the beta. It would be very nice to have though for the beta since this would make testing XB outside of Drupal CMS / other pre-defined setup much easier.

Rebased the sole commit on top of 1.x. Adopted the access check 📌 [PP-1] Update `experience_builder.(experience_builder|api.layout.get) routes` to respect content entity update/field edit access of edited XB field Active added (yay!)

From a back-end POV, this mostly just needs tests — see the @todo in tests/src/Kernel/Controller/ExperienceBuilderControllerTest.php.

Per #4 — we could land this as-is IMHO, and then just let the front-end folks make the necessary changes in a subsequent MR to not fetch the edited entity's component tree (because there's no entity in this context).

I've updated some tests that were failing, updated the access check to account for the new route and added to the test.

Now that we're effectively in beta, changing route names requires a BC layer

I haven't reviewed the MR to have an opinion on whether or not we should change the route names. But if it seems like the new names are better, then we can do so without providing a BC layer. For XB, beta only means data stability, not API stability.