Remove vendors.js as a frontend dependency

[Aljullu]

Depends on #746.

This PR:

• Removes vendors.js as a frontend dependency.
• Uses externals for dependencies, so they are shared between plugins and blocks.
• Merges packages.js and vendors.js files. They were split so vendors.js could be included in the frontend, but that is no longer necessary.

How to test the changes in this Pull Request:

Test vendors.js is no longer a dependency:

1. Create a post and add a Product Categories List block.
2. Open the post in the frontend and verify it works as expected.
3. In the Network tab of your browser devtools, verify no vendors.js file was loaded.

Test we are using externals

1. Install Jetpack.
2. Create a post and add a Product Categories List block, a Slideshow block and a Map block.
3. Open the post in the frontend and, in the Network tab of your browser devtools, verify only one lodash.js file was loaded.

Changelog

Use externals for frontend dependencies so they are shared between extensions and blocks. That saves 2.57MB on page weight.

[psealock]

Uses externals for dependencies, so they are shared between plugins and blocks.

Looking at the vendors.js compiled code, I still see things like lodash dependency. Only 1 request for lodash.js is made, but the dependency is also shipped in vendors.

externals: [ lodash: 'lodash' ], in the webpack config should remove it from vendors and build the blocks js to look for lodash on the window.

EDIT: on frontend.js compiled code, I do see that lodash is not included:

/***/ "lodash":
/*!**********************************!*\
  !*** external {"this":"lodash"} ***!
  \**********************************/

[Aljullu]

@psealock thanks for taking a look!

EDIT: on frontend.js compiled code, I do see that lodash is not included:

Right, this PR only refers to the frontend. I created a PR to fix this in wp-admin (#753). Do you think we should prioritize that too or we can ship it in the next version (2.4)?

[psealock]

Do you think we should prioritize that too or we can ship it in the next version (2.4)?

I think its an easy win with a few changes to the webpack config (I hope its easy at least), so may as well try to get it in.

[psealock]

Looking good! Nice improvement here. Do you have a before/after file size? It might be nice to include in the release notes.

[Aljullu]

I think its an easy win with a few changes to the webpack config (I hope its easy at least), so may as well try to get it in.

👍

Looking good! Nice improvement here. Do you have a before/after file size? It might be nice to include in the release notes.

Basically it saves 2.57MB of vendors.js because externals were included anyway (even though they were not being used). I added the number to the changelog entry.