Tools: Fix running build scripts on Windows does not generate CSS files for blocks

Starting with WordPress 6.0, when running `npm run build` or `npm run build:dev`, no CSS files were generated for the blocks within `wp-includes/blocks/**`.

Props wildworks, clorith, sergeybiryukov.
Fixes #56616.



git-svn-id: https://develop.svn.wordpress.org/trunk@54307 602fd350-edb4-49c9-b593-d223f7449a82

tools/webpack/shared.js

@@ -69,8 +69,12 @@ const stylesTransform = ( mode ) => ( content ) => {
 	return content;
 };
 
+const normalizeJoin = ( ...paths ) => join( ...paths ).replace( /\\/g, '/' );
+
+
 module.exports = {
 	baseDir,
 	baseConfig,
+	normalizeJoin,
 	stylesTransform,
 };