Add Special:ChangeContentModel

Authored by Legoktm.


Add Special:ChangeContentModel

Special:ChangeContentModel allows for users with the 'editcontentmodel'
right to change the content model of a page.

Visiting Special:ChangeContentModel will contain an input field for a
page title. The user will then be sent to
Special:ChangeContentModel?pagetitle=<input> where the page title is
read only, with a content model selector and optional reason field.

The special page only allows converting between content models that
extend TextContent for simplicity. Advanced conversions should be done
via the API.

All content model changes via the special page or API generate a null
revision in the page history and a log entry at
Special:Log/contentmodel. The log entry has a revert link for
convenience (like the move log).

Bug: T72592
Co-Authored-By: Lewis Cawte <lewis@lewiscawte.me>
Change-Id: I296a67c09fcbc880c8c3a648eb5086580725ea46