Create new script enforcing npm pack over yarn pack

- Per Greg's eagle eyes, `yarn pack` was failing to bundle/include the `src/test/` folder somehow and causing test failures for plugins in Kibana trying to import `lib/test/` helpers

- `npm pack` doesn't have this issue, so I opted to create a new command that enforces npm pack over yarn pack

package.json

@@ -17,6 +17,7 @@
     "sync-docs": "node ./scripts/docs-sync.js",
     "build-docs": "cross-env BABEL_MODULES=false cross-env NODE_ENV=production NODE_OPTIONS=--max-old-space-size=4096 webpack --config=src-docs/webpack.config.js",
     "build": "yarn extract-i18n-strings && node ./scripts/compile-clean.js && node ./scripts/compile-eui.js && node ./scripts/compile-scss.js $npm_package_name",
+    "build-pack": "yarn build && npm pack",
     "compile-icons": "node ./scripts/compile-icons.js && prettier --write --loglevel=warn \"./src/components/icon/assets/**/*.js\"",
     "extract-i18n-strings": "node ./scripts/babel/fetch-i18n-strings",
     "lint": "yarn tsc --noEmit && yarn lint-es && yarn lint-sass",

wiki/component-development.md

@@ -60,7 +60,7 @@ Note that `yarn link` currently does not work with Kibana. You'll need to manual
 #### In EUI run:
 
 ```bash
-yarn build && yarn pack
+yarn build-pack
 ```
 
 This will create a `.tgz` file with the changes in your EUI directory. At this point you can move it anywhere.