Editor: Set new default rendering mode for Pages

[Mamaduka]

Supersedes: #7129
Gutenberg PR: WordPress/gutenberg#68549

This update updates the page post-type definition and sets template-locked as the new default rendering mode for the block editor.

Trac ticket: https://core.trac.wordpress.org/ticket/61811

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[TylerB24890]

Thanks for the fixes! 😃

[Mamaduka]

I'm considering making the new default mode for Pages conditional and only setting it when wp_is_block_theme is true. Why?

• The users get the most out of this rendering mode when using block themes.
• It will eventually work for hybrid themes, but there are some known issues that I'm not sure we can resolve for WP 6.8 (but I'll try my best). See Wrong template displayed for hybrid themes in the post template editor gutenberg#64341.
• This is also the original direction, which got lost during refactorings. See Feature: Set editor rendering mode by post type gutenberg#62304.

Is the create_initial_post_types (still) the best place to enable the new default mode for Pages based on conditions? cc @swissspidy, @peterwilsoncc

[swissspidy]

Yes, I don't see why not. Given that create_initial_post_types runs on init, it should be safe to use wp_is_block_theme() at that point.

[audrasjb]

I'm considering making the new default mode for Pages conditional and only setting it when wp_is_block_theme is true.

Anyway, I think it would be safer to implement this step by step, and perhaps not making it the default behavior for page-like post types for now, at least in hybrid/classic themes.

[Mamaduka]

Synced the latest changes from WordPress/gutenberg#69160. This is ready for testing and approval.

[Mamaduka]

Suggested change

	if ( wp_is_block_theme() ) {
	if ( wp_is_block_theme() && current_theme_supports( 'block-templates' ) ) {

I think I'll need to harden this condition by adding a current_theme_supports check. While it should be an edge case for a block theme not to support block-templates, it's still technically doable. See: WordPress/gutenberg#67875 (comment).