Build: Base webpack.config.js on calypso-build's

[ockham]

Changes proposed in this Pull Request:

Build: Base webpack.config.js on calypso-build's

This allows us to remove a few now-redundant Gulp tasks, since calypso-build takes care of e.g. minification, building CSS from SCSS, and RTL for us automatically.

Testing instructions:

yarn distclean && yarn
yarn build-client

Builds without errors?

yarn docker:up

Smoke-test the React Dashboard. Watch the browser console for errors.

Also try

yarn clean-client && NODE_ENV=production yarn build-client

and verify that _inc/build/admin.js is minified.

Proposed changelog entry for your changes:

• Build: Base webpack.config.js on calypso-build's

[jetpackbot]

Thank you for the great PR description!

When this PR is ready for review, please apply the [Status] Needs Review label. If you are an a11n, please have someone from your team review the code if possible. The Jetpack team will also review this PR and merge it to be included in the next Jetpack release.

Scheduled Jetpack release: June 4, 2019.
Scheduled code freeze: May 28, 2019

Generated by 🚫 dangerJS against 68c3444

[simison]

With this, we can probably get rid of Gulp task building styles for the dash, and use Webpack css pipeline instead:

jetpack/tools/builder/sass.js

Lines 19 to 33 in 9bc1f0e

	gulp.task( 'sass:dashboard', function( done ) {
	log( 'Building Dashboard CSS bundle...' );
	return gulp
	.src( './_inc/client/scss/style.scss' )
	.pipe( sass( { outputStyle: 'compressed' } ).on( 'error', sass.logError ) )
	.pipe( banner( '/* Do not modify this file directly. It is compiled SASS code. */\n' ) )
	.pipe( autoprefixer() )
	.pipe( rename( { suffix: '.min' } ) )
	.pipe( gulp.dest( './_inc/build' ) )
	.on( 'end', function() {
	log( 'Dashboard CSS finished.' );
	doRTL( 'main', done );
	} );
	} );

That doesn't have to happen in this PR, tho.

[matticbot]

Caution: This PR has changes that must be merged to WordPress.com
Hello ockham! These changes need to be synced to WordPress.com - If you 're an a11n, please commandeer, review, and approve D28250-code before merging this PR. Thank you!

[ockham]

Blocked by #12381

[matticbot]

ockham, Your synced wpcom patch D28250-code has been updated.

[matticbot]

ockham, Your synced wpcom patch D28250-code has been updated.

[zinigor]

I'm happy to see all the custom stuff slowly disappearing and being replaced by common build tools, thanks for working on this!
Works well for me both in dev and prod environments.