Themes: Auto-enable block-templates support for all block themes.

Block themes without theme.json file used to have block-templates support disabled.
This commit brings this in sync with the behavior in the gutenberg plugin.

See #54335.

Built from https://develop.svn.wordpress.org/trunk@52347


git-svn-id: http://core.svn.wordpress.org/trunk@51939 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/theme-templates.php

@@ -211,7 +211,7 @@ function the_block_template_skip_link() {
  * @since 5.8.0
  */
 function wp_enable_block_templates() {
-	if ( WP_Theme_JSON_Resolver::theme_has_support() ) {
+	if ( wp_is_block_theme() || WP_Theme_JSON_Resolver::theme_has_support() ) {
 		add_theme_support( 'block-templates' );
 	}
 }