Projects administration page: no bulk enable and disable, no orphan string warning

Problem

The Drupal 7 projects administration page is a form: every project has an "Enabled" checkbox, one "Save changes" toggles them in bulk, and while orphan source strings exist the page warns about them, links to the cleanup and offers no "Delete" links, since deleting a project with orphans around would take the orphans of other projects with it.

On 3.0.x the page is the plain entity listing: the status is a number column, projects are enabled one by one on their edit forms, and nothing warns about orphan strings.

Proposed resolution

The project list builder becomes a form like on Drupal 7: an "Enabled" checkbox per project with "Save changes", the orphan warning with the cleanup link, and no delete operation while orphans exist. The other columns and operations stay.

Tests

Drupal 7 first: L10nServerProjectListTestCase checks the links and checkboxes, disables and enables a project in bulk, and checks the orphan warning, the missing delete links and their return after the cleanup. (On Drupal 7 the warning is set while the listing renders, after the messages of the page, so it shows on the next page.) Ported as ProjectListTest.

LLM disclosure

LLM was used to find, diagnose explain and fix this issue. With human review.