Update Node LTS 12 (attempt 2)

[sirreal]

Node v12 is now LTS. Use it.

Reverts #37298

[matticbot]

Test live: https://calypso.live/?branch=revert-37298-revert-37031-update/node-lts-12

[matticbot]

Test live: https://calypso.live/?branch=revert-37298-revert-37031-update/node-lts-12

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

App Entrypoints (~44111 bytes added 📈 [gzipped])

name                   parsed_size           gzip_size
entry-gutenboarding      +186966 B  (+7.5%)   +44114 B  (+6.8%)
entry-main                   -93 B  (-0.0%)       +0 B
entry-login                  -93 B  (-0.0%)       -1 B  (-0.0%)
entry-domains-landing        -93 B  (-0.0%)       -2 B  (-0.0%)

Common code that is always downloaded and parsed every time the app is loaded, no matter which route is used.

Sections (~8 bytes added 📈 [gzipped])

name              parsed_size           gzip_size
gutenberg-editor        +78 B  (+0.0%)      +21 B  (+0.0%)
woocommerce             -18 B  (-0.0%)      -13 B  (-0.0%)

Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Async-loaded Components (~340 bytes removed 📉 [gzipped])

name                                 parsed_size           gzip_size
async-load-lib-happychat-connection       +222 B  (+0.3%)     -340 B  (-1.9%)

React components that are loaded lazily, when a certain part of UI is displayed for the first time.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[sirreal]

I think the conclusion of investigation is that we should just try this again. @Automattic/team-calypso y'all approve?

[blowery]

@sirreal yup, give it another shot