build(js,css): add browserslist spec and update JS and CSS toolchains

[mcous]

overview

Following up on our cross-browser support discussion(s), this PR implements JS polyfilling and improves out CSS polyfilling support

DO NOT MERGE until after PD's next release PD release, merge unblocked

changelog

• Adds a .browserslistrc file to specify our JS and CSS polyfill support
• Adds @babel/preset-env polyfilling via core-js to our three main web-apps (app, PD, LL)
• Upgrades JS / CSS build toolchains across the board
• Switches off the discontinues cssnext to postcss-preset-env
• Makes a few code changes to support the toolchain changes
  • CSS color function renamed to color-mod
  • stable module added for guaranteed stable array sorting in discovery-client
    • Array.prototype.sort is not guaranteed stable and the addition of core-js was somehow exposing this and causing tests to go flakey

review requests

This is marked as do not merge until the planned bugfix release of PD goes out at the end of this week. Everything looks good in my cursory checking, but given the kinds of changes this PR makes, App, PD, and LL should really go through each of their full QA suites before the next release with this change.

The best testing you can do is just stress testing. Be on the lookout for:

• Weird errors in the console that weren't there before
• Colors or other styles not getting applied properly
• Unexpected white-screens
• Unexpected test failures, flakey or otherwise

[codecov]

Codecov Report

Merging #4083 into edge will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##             edge    #4083      +/-   ##
==========================================
+ Coverage   57.24%   57.24%   +<.01%     
==========================================
  Files         850      850              
  Lines       24004    24002       -2     
==========================================
  Hits        13741    13741              
+ Misses      10263    10261       -2

Impacted Files	Coverage Δ
babel.config.js	0% <ø> (ø)	⬆️
discovery-client/src/service-list.js	100% <100%> (ø)	⬆️

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[IanLondon]

code looks good, PD and LL+LC both seem like they're working fine and everything looks the same to me, no new console messages. Couldn't find any missed color(s in CSS of PD/App/LL.

[Kadee80]

• RA layout/colors appear unaffected
• LL and LC layout/colors appear unaffected
• CompLib layout/colors appear unaffected