Use data, element packages directly from GB folder

Edit the files in the `build/` subfolders directly to have hot-reload
work. If you change the ones in `src/` then the packages need to be
rebuilt via GB (npm run build:packages).

* Metro does its magic here and finds the packages directly in the
gutenberg/packages folder automagically
* Jest needs to be configured to find them (mapping)
* Flow needs configuration too

.flowconfig

@@ -82,6 +82,8 @@ munge_underscores=true
 
 module.name_mapper='^[./a-zA-Z0-9$_-]+\.\(bmp\|gif\|jpg\|jpeg\|png\|psd\|svg\|webp\|m4v\|mov\|mp4\|mpeg\|mpg\|webm\|aac\|aiff\|caf\|m4a\|mp3\|wav\|html\|pdf\)$' -> 'RelativeImageStub'
 module.name_mapper='@gutenberg' -> '<PROJECT_ROOT>/gutenberg'
+module.name_mapper='@wordpress/data' -> '<PROJECT_ROOT>/gutenberg/packages/data'
+module.name_mapper='@wordpress/element' -> '<PROJECT_ROOT>/gutenberg/packages/element'
 
 ; mock/ignore style files
 module.name_mapper='.*\(.scss\)' -> 'empty/object'

jest.config.js

@@ -31,6 +31,7 @@ module.exports = {
 	],
 	moduleNameMapper: {
 		'@wordpress\\/(blocks|editor)$': '<rootDir>/gutenberg/$1',
+		'@wordpress\\/(data|element|deprecated)$': '<rootDir>/gutenberg/packages/$1',
 		'@gutenberg': '<rootDir>/gutenberg',
 
 		// Mock the CSS modules. See https://facebook.github.io/jest/docs/en/webpack.html#handling-static-assets

rn-cli.config.js

@@ -1,5 +1,4 @@
 /** @format */
-const blacklist = require( 'metro' ).createBlacklist;
 
 const enm = require( 'node-libs-react-native' );
 enm.fs = __dirname + '/__mocks__/nodejsMock.js';
@@ -8,9 +7,6 @@ enm.canvas = __dirname + '/__mocks__/nodejsMock.js';
 
 module.exports = {
 	extraNodeModules: enm,
-	getBlacklistRE: function() {
-		return blacklist( [ /gutenberg\/packages\/.*/ ] );
-	},
 	getTransformModulePath() {
 		return require.resolve( './sass-transformer.js' );
 	},