Build: Dynamically pick JS/CSS build files for ZIP gen

[mcsf]

Description

Sparked by #5430 (comment), this aims to reduce the need for manual synchronization between webpack.config.js, bin/build-plugin-zip.sh, .eslintrc.js, and any other place where knowledge of which entry points Gutenberg has is needed.

To keep it short, this PR only targets bin/build-plugin-zip.sh and uses the shell's ** file expansion.

Previously

An initial exploration saw the creation of a small bin/list-entry-points.js script which read webpack.config.js (thus treating it as the canonical source for entry-point information) and roughly did:

$entry_points=$(bin/list-entry-points.js | tr \\n , | sed 's/,$//') # comma-separated list
$build_files=$(eval echo {$entry_points}/build/*.{js,css) # actually wrong, because `*.css* will emerge whenever a proper CSS file is missing

#!/usr/bin/env node
// For reference, here's bin/list-entry-points.js

const config = require( '../webpack.config.js' );

Object.keys( config.externals )
	// Filter out other externals, keep entry points
	.filter( k => k.indexOf( '@wordpress/' ) >= 0 )
	// Remove the '@wordpress/' prefix
	.map( k => k.substr( 11 ) )
	// Fix key 'editPost,edit-post'
	.map( k => k.indexOf( 'editPost' ) >= 0 ? 'edit-post' : k )
	.forEach( k => console.log( k ) );

How Has This Been Tested?

Run ./bin/build-plugin-zip.sh. Make sure no errors are found. Inspect the generated ZIP file. Compare its manifesto (e.g. unzip -l <file>) with the one from the latest release or one generated from master.

Screenshots (jpeg or gifs if applicable):

Types of changes

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code has proper inline documentation.

[mcsf]

I don't believe the *.{js,map} bit was up-to-date. In any case, we don't expect .map files in the ZIP file, to my knowledge. Hence my removal.

[aduth]

👍

Rebased to resolve conflicts.

While this makes bundling less intentional (we were previously targeting specific folders where we expect CSS to exist), I think it lends to better overall maintainability.

[mcsf]

While this makes bundling less intentional (we were previously targeting specific folders where we expect CSS to exist)

Agreed. I can see this sort of work progress into clearly defining our entry points and leveraging said definition throughout the project.