Themes: Make block themes support HTML5 by default.

For block themes, [52369] added HTML5 support for `'comment-list'`, `'comment-form'`, `'style'`, and `'script'`. However, when sites upgrade to 5.9 with non-block content such as a gallery and caption, the markup was not HTML5. 

This commit adds full HTML5 theme feature support for block themes. Non-block content such as a `[gallery]` and `[caption]` shortcodes will natively be in HMTL5 markup without block themes needing to specifically add `add_theme_support( 'html5, .. )` to the theme. 

Follow-up to [24417], [27302], [34261], [52369], [52383], [52386].

Props @joyously, costdev, hellofromTonya, audrasjb, Mamaduka, ocean90.
Fixes #54731. See #54597.
Built from https://develop.svn.wordpress.org/trunk@52439


git-svn-id: http://core.svn.wordpress.org/trunk@52031 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/theme.php

@@ -4181,7 +4181,12 @@ function _add_default_theme_supports() {
 	add_theme_support( 'post-thumbnails' );
 	add_theme_support( 'responsive-embeds' );
 	add_theme_support( 'editor-styles' );
-	add_theme_support( 'html5', array( 'comment-form', 'comment-list', 'style', 'script' ) );
+	/*
+	 * Makes block themes support HTML5 by default for the comment block and search form
+	 * (which use default template functions) and `[caption]` and `[gallery]` shortcodes. 
+	 * Other blocks contain their own HTML5 markup.
+	 */
+	add_theme_support( 'html5', array( 'comment-form', 'comment-list', 'search-form', 'gallery', 'caption', 'style', 'script' ) );
 	add_theme_support( 'automatic-feed-links' );
 
 	add_filter( 'should_load_separate_core_block_assets', '__return_true' );

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-beta4-52438';
+$wp_version = '5.9-beta4-52439';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.