Editor: Revert new default rendering mode for Pages

[Mamaduka]

Important

I want to highlight that limiting the ability to edit template parts in template-locked rendering mode is an intentional choice and isn't a bug.

Unfortunately, this can make the new default rendering mode confusing in some instances and prevent users from editing a post/page title.

PR reverts the new default rendering mode for Pages (WP-61811).

I'm not restoring the special case for the Site Editor, where the rendering mode was different from that of the Post Editor. Why?

• Consistency - The new default's goal was to make the page editing experience consistent between the post and site editors. There should be only one default rendering mode per post type across the editors.
• User preferences - The new persistent user preference allows users to set rendering mode based on their needs.
• More logic, more problems - I don't want to complicate the logic for deriving the default rendering mode.

Trac ticket: https://core.trac.wordpress.org/ticket/63139

[github-actions]

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Props mamaduka, joemcgill.

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[github-actions]

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[joemcgill]

As much as I think folks will like this feature, opting in by default does create enough friction in real use cases that it probably does make sense to remove.

All the infrastructure is still in place for people to opt in to this default by modifying post type support for any post types that where they want this to be the default experience and when users change their template view while editing a post, that preference will be used the next time that user edits a post of the same post type, so this has been a worthwhile experiment, leading to some real improvements in the UX.

Thanks @Mamaduka!

[github-actions]

A commit was made that fixes the Trac ticket referenced in the description of this pull request.

SVN changeset: 60076
GitHub commit: 2bf5a23

This PR will be closed, but please confirm the accuracy of this and reopen if there is more work to be done.