Offer Template:Start ... pages when a new article is created

[bonelifer]

Part 3 of the template quality-of-life work. When someone creates a new article, the edit page now offers the templates meant as starting points.

• The choice. For an article that does not exist yet, a Start from row above the edit form lists "A blank article" and every live template whose name starts with Start (Template:Start Extension is shown as "Extension"). Use reloads the form with the text box filled with that template's text, without its <noinclude> parts, to edit and save as the new article. It is a plain GET form, so it works without JavaScript.
• The text is copied, not included, so later edits to a template do not change articles made from it.
• It is shown only for a new article, and only when at least one start template exists. An existing article shows no choice and ignores the parameter. Only templates named Start ... can be used this way; any other name gives an empty box.
• The live-version query that finds the templates is shared with the templates list page.
• There is no separate admin page: the start templates are ordinary wiki pages with versions, approval and permissions. README and the TODO plan are updated.
• New strings are in the English language file only.

Tests

• Unit tests: 223 tests, 522 assertions, all pass. New case for start-template names, case and refusing non-start templates.
• A new browser test passes 10 of 10 on phpBB 3.3.19 with SQLite, 4.0.0-a3-dev with SQLite, MySQL 8.0 and PostgreSQL 16: no choice without start templates, the options, filling the text box exactly (including &, a table and BBCode), no copy of the <noinclude> part, saving the new article, refused non-start and missing templates, and no choice on an existing article.
• The template list, template page and template browser tests still pass on MySQL, and the rows test on 4.0.

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Investigated and written by Claude on behalf of William Jacoby (bonelifer).