Build: Webpack instead of Browserify as JavaScript bundler.

Use Webpack as our bundler of choice, enabling improved JavaScript build chain capabilities.

Props aduth, netweb, kadamwhite, schlessera.
Fixes #40894. 


git-svn-id: https://develop.svn.wordpress.org/trunk@41752 602fd350-edb4-49c9-b593-d223f7449a82

webpack.config.dev.js

@@ -0,0 +1,21 @@
+var path         = require( 'path' ),
+	SOURCE_DIR   = 'src/',
+	mediaConfig  = {},
+	mediaBuilds  = [ 'audiovideo', 'grid', 'models', 'views' ],
+	webpack      = require( 'webpack' );
+
+
+mediaBuilds.forEach( function ( build ) {
+	var path = SOURCE_DIR + 'wp-includes/js/media';
+	mediaConfig[ build ] = './' + path + '/' + build + '.manifest.js';
+} );
+
+module.exports = {
+	cache: true,
+	watch: true,
+	entry: mediaConfig,
+	output: {
+		path: path.join( __dirname, 'src/wp-includes/js' ),
+		filename: 'media-[name].js'
+	}
+};