Add a moderation state pseudo field on the view mode

Problem/Motivation

If site builders don't want to allow editing the Moderation state on the View page, they have no option out-of-the-box to show the current node state.

Furthermore, having the Moderation control form on the View page of a node can be confusing and degrade performance (less cacheability & easier to spam transitions without actually editing the node).

Proposed resolution

I suggest we create a new pseudo-field by default, "Moderation state", to enable site builders to just show the node's state on the Manage display tab. This can be enough to alert the node's author that he might want/need to edit the content & it's state.

An alternative approach could be to add an option on the existing Moderation control field (on the Manage display tab) to only show the state (and leave the transition selection on the edit forms), or actually a boolean to enable/disable the moderation control form.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet