Build/Test Tools: Add MySQL 8.4 support to the Docker environment.

Because `caching_sha2_password` is not supported on PHP 7.2 & 7.3, the local Docker environment has used the `--default-authentication-plugin` system variable to always make use of `mysql_native_password` despite MySQL 8.0 deprecating this auth plugin.

However in MySQL 8.4, the `--default-authentication-plugin` option was removed in favor of `--authentication-policy`, and `mysql_native_password` is now disabled by default. `mysql_native_password` has also been removed in MySQL 9.0.

This change adds support to the local Docker environment for MySQL 8.4 by adding some helper functions that determine which authentication plugin should be used based on the configured PHP/MySQL versions and automatically making the necessary configuration adjustments. 

Reviewed by peterwilsoncc. 
Merges [59279] to the 6.7 branch.

Props ayeshrajans, johnbillion, aristath, jorbin.
See #61218.
Built from https://develop.svn.wordpress.org/branches/6.7@59309


git-svn-id: http://core.svn.wordpress.org/branches/6.7@58695 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.7-RC1-59308';
+$wp_version = '6.7-RC1-59309';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.