General: Memoize the return value in wp_get_wp_version().

This aims to optimize performance by saving the return value to a static variable, so that the `version.php` file is not unnecessarily required on each function call.

Follow-up to [58813].

Props Cybr, debarghyabanerjee, mukesh27.
Fixes #61782. See #61627.

git-svn-id: https://develop.svn.wordpress.org/trunk@58827 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/functions.php

@@ -8819,7 +8819,11 @@ function clean_dirsize_cache( $path ) {
  * @return string The current WordPress version.
  */
 function wp_get_wp_version() {
-	require ABSPATH . WPINC . '/version.php';
+	static $wp_version;
+
+	if ( ! isset( $wp_version ) ) {
+		require ABSPATH . WPINC . '/version.php';
+	}
 
 	return $wp_version;
 }