Templates: Deprecate _inject_theme_attribute_in_block_template_content.

It can be replaced by passing `_inject_theme_attribute_in_template_part_block` as second argument to `traverse_and_serialize_blocks()`.

Per WordPress 6.4 Beta 1, there aren't going to be any more calls in Core to `_inject_theme_attribute_in_block_template_content()`.

Note that `_inject_theme_attribute_in_block_template_content` has always had `@access private` set in its PHPDoc.

Props gziolo.
Fixes #59452.

git-svn-id: https://develop.svn.wordpress.org/trunk@56719 602fd350-edb4-49c9-b593-d223f7449a82

Author: ockham

src/wp-includes/block-template-utils.php

@@ -475,12 +475,19 @@ function _flatten_blocks( &$blocks ) {
  * stylesheet as a theme attribute into each wp_template_part
  *
  * @since 5.9.0
+ * @deprecated 6.4.0 Use traverse_and_serialize_blocks( parse_blocks( $template_content ), '_inject_theme_attribute_in_template_part_block' ) instead.
  * @access private
  *
  * @param string $template_content serialized wp_template content.
  * @return string Updated 'wp_template' content.
  */
 function _inject_theme_attribute_in_block_template_content( $template_content ) {
+	_deprecated_function(
+		__FUNCTION__,
+		'6.4.0',
+		'traverse_and_serialize_blocks( parse_blocks( $template_content ), "_inject_theme_attribute_in_template_part_block" )'
+	);
+
 	$has_updated_content = false;
 	$new_content         = '';
 	$template_blocks     = parse_blocks( $template_content );

tests/phpunit/tests/block-template-utils.php

@@ -311,6 +311,13 @@ public function test_not_inject_theme_attribute_non_template_part_block() {
 		);
 	}
 
+	/**
+	 * @ticket 59452
+	 *
+	 * @covers ::_inject_theme_attribute_in_block_template_content
+	 *
+	 * @expectedDeprecated _inject_theme_attribute_in_block_template_content
+	 */
 	public function test_inject_theme_attribute_in_block_template_content() {
 		$theme                           = get_stylesheet();
 		$content_without_theme_attribute = '<!-- wp:template-part {"slug":"header","align":"full", "tagName":"header","className":"site-header"} /-->';