Allow Drupal\Core to provide [config] entity types

This ain't really possible to test unless we convert an existing config entity. In many ways action, date format and menu should be in core and not system but that is one heck of a change in terms of config object name change (all existing site would break).

So if we do want to split this off from #2283977: Create a new ConfigEntity type for storing bundle-specific customizations of base fields then this will have to be another beta blocker too. Since this blocks that. Here's the patch if we want to go ahead.

Other candidates would be entity view/form displays ?

An advantage of moving something provided by the entity module is that it also unblocks the issue to de-module-ify entity again.

Based on the discussions in #2295469: Add support for static permission definitions with *.permissions.yml and #2088371: YAML discovery incompatible with translations I'd recommend looking into system_permission() for now, though Gábor also indicated one-off translation for YAYAML (Yet Another YAML) wouldn't be much worse than anything else. But hook_permission() does just work. It's ugly and non-ideal, but it could be fixed in a followup or not.

I think system_permission() is totally fine. I guess in this case we are not adding tests because we'll do in #2283977: Create a new ConfigEntity type for storing bundle-specific customizations of base fields soon and otherwise not possible here?

Yeah we can't add a specific test for this unfortunately. But the moment it is use it is tested :)

All righto, looks good to me. The entity module demodulifying will have to deal with the permission then (in #2031717: Make entity module not required) as far as I understand so this one is good.

Committed to 8.x. Thanks. It's a bit of a hack but I think we can make an exception to allow for the beta blockers to make progress.