Build tools: Use Webpack splitChunks feature to extract duplicated babel runtime

[gziolo]

Description

I followed Webpack docs: https://webpack.js.org/plugins/split-chunks-plugin/.

It looks like this decresases the size of the bundles produced by Webpack by ~25%. I need to calculate it again. It would be great to use some tools instead :)

Todo tasks and open questions

• Fix different chunk name for development (build/babel-runtime/babel-runtime.index.js) and production (build/babel-runtime/0.index.js)
• How to enable those polyfills for all individual modules? Include them everywhere? This is what this PR does at the moment

Before

                                       Asset       Size  Chunks                    Chunk Names
                     ./build/blocks/index.js    225 KiB      23  [emitted]         blocks
                  ./build/wordcount/index.js     10 KiB       0  [emitted]         wordcount
                        ./build/url/index.js   20.6 KiB       2  [emitted]         url
                 ./build/token-list/index.js   16.1 KiB       3  [emitted]         tokenList
                  ./build/shortcode/index.js   16.2 KiB       4  [emitted]         shortcode
              ./build/redux-routine/index.js   18.6 KiB       5  [emitted]         reduxRoutine
                    ./build/plugins/index.js   24.5 KiB       6  [emitted]         plugins
                        ./build/nux/index.js   27.6 KiB       7  [emitted]         nux
                   ./build/keycodes/index.js   14.8 KiB       8  [emitted]         keycodes
           ./build/is-shallow-equal/index.js   1.15 KiB       9  [emitted]         isShallowEqual
                       ./build/i18n/index.js   27.4 KiB      10  [emitted]         i18n
              ./build/html-entities/index.js  986 bytes      11  [emitted]         htmlEntities
                      ./build/hooks/index.js   19.3 KiB      12  [emitted]         hooks
                    ./build/element/index.js     39 KiB      13  [emitted]         element
                     ./build/editor/index.js    340 KiB      14  [emitted]  [big]  editor
                  ./build/dom-ready/index.js  778 bytes      15  [emitted]         domReady
                        ./build/dom/index.js   22.6 KiB      16  [emitted]         dom
                 ./build/deprecated/index.js   10.8 KiB      17  [emitted]         deprecated
                       ./build/date/index.js    192 KiB      18  [emitted]         date
                       ./build/data/index.js   66.1 KiB      19  [emitted]         data
                  ./build/core-data/index.js   75.3 KiB      20  [emitted]         coreData
                    ./build/compose/index.js   32.4 KiB      21  [emitted]         compose
                   ./build/viewport/index.js   24.3 KiB       1  [emitted]         viewport
                       ./build/blob/index.js  909 bytes      24  [emitted]         blob
                      ./build/autop/index.js   29.3 KiB      25  [emitted]         autop
                  ./build/api-fetch/index.js   40.6 KiB      26  [emitted]         apiFetch
                       ./build/a11y/index.js   5.32 KiB      27  [emitted]         a11y
                ./build/core-blocks/index.js  994 bytes      28  [emitted]         coreBlocks
              ./build/block-library/index.js    209 KiB      29  [emitted]         blockLibrary
                  ./build/edit-post/index.js   85.1 KiB      30  [emitted]         editPost
                 ./build/components/index.js    500 KiB      31  [emitted]  [big]  components

./build/block-serialization-spec-parser/index.js 9.48 KiB 22 [emitted] blockSerializationSpecParser

Total: ~2 100 kB (before gzip)

After

                                       Asset       Size                        Chunks                    Chunk Names
           ./build/is-shallow-equal/index.js   1.15 KiB                isShallowEqual  [emitted]         isShallowEqual
                       ./build/a11y/index.js   2.36 KiB                          a11y  [emitted]         a11y
                      ./build/autop/index.js   6.43 KiB                         autop  [emitted]         autop
./build/babel-runtime/babel-runtime.index.js   75.8 KiB                 babel-runtime  [emitted]         babel-runtime
                       ./build/blob/index.js  909 bytes                          blob  [emitted]         blob
              ./build/block-library/index.js    173 KiB                  blockLibrary  [emitted]         blockLibrary
                     ./build/blocks/index.js    178 KiB                        blocks  [emitted]         blocks
                 ./build/components/index.js    451 KiB                    components  [emitted]  [big]  components
                    ./build/compose/index.js   6.17 KiB                       compose  [emitted]         compose
                ./build/core-blocks/index.js  992 bytes                    coreBlocks  [emitted]         coreBlocks
                  ./build/core-data/index.js   24.5 KiB                      coreData  [emitted]         coreData
                       ./build/data/index.js   21.5 KiB                          data  [emitted]         data
                       ./build/date/index.js    188 KiB                          date  [emitted]         date
                 ./build/deprecated/index.js   1.69 KiB                    deprecated  [emitted]         deprecated
                        ./build/dom/index.js   7.57 KiB                           dom  [emitted]         dom
                  ./build/dom-ready/index.js  778 bytes                      domReady  [emitted]         domReady
                  ./build/edit-post/index.js   53.8 KiB                      editPost  [emitted]         editPost
                     ./build/editor/index.js    288 KiB                        editor  [emitted]  [big]  editor
                    ./build/element/index.js    6.9 KiB                       element  [emitted]         element
                      ./build/hooks/index.js   4.99 KiB                         hooks  [emitted]         hooks
              ./build/html-entities/index.js  986 bytes                  htmlEntities  [emitted]         htmlEntities
                       ./build/i18n/index.js   19.2 KiB                          i18n  [emitted]         i18n
                  ./build/api-fetch/index.js    4.1 KiB                      apiFetch  [emitted]         apiFetch
                   ./build/keycodes/index.js   3.48 KiB                      keycodes  [emitted]         keycodes
                        ./build/nux/index.js   6.92 KiB                           nux  [emitted]         nux
                    ./build/plugins/index.js   4.21 KiB                       plugins  [emitted]         plugins
              ./build/redux-routine/index.js   1.75 KiB                  reduxRoutine  [emitted]         reduxRoutine
                  ./build/shortcode/index.js   4.14 KiB                     shortcode  [emitted]         shortcode
                 ./build/token-list/index.js   2.52 KiB                     tokenList  [emitted]         tokenList
                        ./build/url/index.js   8.86 KiB                           url  [emitted]         url
                   ./build/viewport/index.js   2.86 KiB                      viewport  [emitted]         viewport
                  ./build/wordcount/index.js    3.1 KiB                     wordcount  [emitted]         wordcount

./build/block-serialization-spec-parser/index.js 9.48 KiB blockSerializationSpecParser [emitted] blockSerializationSpecParser

Total: ~1 580 kB (before gzip)

How has this been tested?

Checklist:

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

[gziolo]

I fixed the issue with the name of the chunk which collects all Babel related dependencies:

• @babel/runtime-corejs2
• core-js
• regenerator-runtime

Kudos to @jsnajdr for the great hint 👍

[gziolo]

An alternative solution was proposed by @aduth in #9643. Let's focus on that one instead.