Block Editor: Add a script to run Gutenberg end 2 end tests on Core.

The script is not part of CI yet because the job takes 40mn to run
and it's not useful in all PRs/commits.

Fixes #50469.


git-svn-id: https://develop.svn.wordpress.org/trunk@48382 602fd350-edb4-49c9-b593-d223f7449a82

tools/webpack/packages.js

@@ -250,6 +250,9 @@ module.exports = function( env = { environment: 'production', watch: false, buil
 			new DefinePlugin( {
 				// Inject the `GUTENBERG_PHASE` global, used for feature flagging.
 				'process.env.GUTENBERG_PHASE': 1,
+				'process.env.FORCE_REDUCED_MOTION': JSON.stringify(
+					process.env.FORCE_REDUCED_MOTION
+				),
 			} ),
 			new LibraryExportDefaultPlugin( [
 				'api-fetch',