Build: Introduce SCRIPT_DEBUG global in webpack processing

Backports the same changes to the webpack config in the Gutenberg plugin with WordPress/gutenberg#50122.

The `warning` function from `@wordpress/warning` no longer worked correctly with webpack 5. In practice, it no longer called `console.warn`. To fix it, the usage of `process.env.NODE_ENV` check got replaced with another optional global: `SCRIPT_DEBUG`. All the tools used in the Gutenberg, get updated to work with this new constant, including `@wordpress/scripts`. This way, developers are able to guard code that should be run only in development mode. In WordPress core, the same constant needs to be added mostly to ensure that the code behind the check gets completely removed in production mode.

Fixes #59407.


Built from https://develop.svn.wordpress.org/trunk@56699


git-svn-id: https://core.svn.wordpress.org/trunk@56211 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.4-alpha-56698';
+$wp_version = '6.4-alpha-56699';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.