Code Modernization: Silence the deprecation warnings for missing return type in WP_Block_List.

This fixes the "Deprecated: Return type of `WP_Block_List::[METHODNAME]()` should be compatible with `ArrayAccess::[METHODNAME](): type`" warnings on PHP 8.1.

PHP native interfaces now have declared return types and methods in classes implementing these interfaces need to either have the return type declared (in a covariant compatible manner with the PHP native interface method declaration), or need to silence the deprecation warning using the `#[ReturnTypeWillChange]` attribute.

Follow-up to [51517], [51529], [51530], [51531].

Props jrf.
See #53635.

git-svn-id: https://develop.svn.wordpress.org/trunk@51532 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-includes/class-wp-block-list.php

@@ -72,6 +72,7 @@ public function __construct( $blocks, $available_context = array(), $registry =
 	 * @param string $index Index of block to check.
 	 * @return bool Whether block exists.
 	 */
+	#[ReturnTypeWillChange]
 	public function offsetExists( $index ) {
 		return isset( $this->blocks[ $index ] );
 	}
@@ -86,6 +87,7 @@ public function offsetExists( $index ) {
 	 * @param string $index Index of block value to retrieve.
 	 * @return mixed|null Block value if exists, or null.
 	 */
+	#[ReturnTypeWillChange]
 	public function offsetGet( $index ) {
 		$block = $this->blocks[ $index ];
 
@@ -107,6 +109,7 @@ public function offsetGet( $index ) {
 	 * @param string $index Index of block value to set.
 	 * @param mixed  $value Block value.
 	 */
+	#[ReturnTypeWillChange]
 	public function offsetSet( $index, $value ) {
 		if ( is_null( $index ) ) {
 			$this->blocks[] = $value;
@@ -124,6 +127,7 @@ public function offsetSet( $index, $value ) {
 	 *
 	 * @param string $index Index of block value to unset.
 	 */
+	#[ReturnTypeWillChange]
 	public function offsetUnset( $index ) {
 		unset( $this->blocks[ $index ] );
 	}
@@ -135,6 +139,7 @@ public function offsetUnset( $index ) {
 	 *
 	 * @link https://www.php.net/manual/en/iterator.rewind.php
 	 */
+	#[ReturnTypeWillChange]
 	public function rewind() {
 		reset( $this->blocks );
 	}
@@ -148,6 +153,7 @@ public function rewind() {
 	 *
 	 * @return mixed Current element.
 	 */
+	#[ReturnTypeWillChange]
 	public function current() {
 		return $this->offsetGet( $this->key() );
 	}
@@ -161,6 +167,7 @@ public function current() {
 	 *
 	 * @return mixed Key of the current element.
 	 */
+	#[ReturnTypeWillChange]
 	public function key() {
 		return key( $this->blocks );
 	}
@@ -172,6 +179,7 @@ public function key() {
 	 *
 	 * @link https://www.php.net/manual/en/iterator.next.php
 	 */
+	#[ReturnTypeWillChange]
 	public function next() {
 		next( $this->blocks );
 	}
@@ -183,6 +191,7 @@ public function next() {
 	 *
 	 * @link https://www.php.net/manual/en/iterator.valid.php
 	 */
+	#[ReturnTypeWillChange]
 	public function valid() {
 		return null !== key( $this->blocks );
 	}
@@ -196,6 +205,7 @@ public function valid() {
 	 *
 	 * @return int Block count.
 	 */
+	#[ReturnTypeWillChange]
 	public function count() {
 		return count( $this->blocks );
 	}