feat: reduce icon file size

[bradenmacdonald]

Description

Currently, the transpiled .js file of each of our icons contains some boilerplate to support extremely old browsers that don't understand the ...spread operator:

function _extends() { _extends = Object.assign ? Object.assign.bind() : function (target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i]; for (var key in source) { if (Object.prototype.hasOwnProperty.call(source, key)) { target[key] = source[key]; } } } return target; }; return _extends.apply(this, arguments); }

This code is not necessary at all, yet it is included in every single icon file, and will be incorporated many times over into the final build. This doesn't actually impact bundle size much in practice because so much redundancy gets heavily compressed by gzip before being sent over the wire. But it's still adding complexity to these files that isn't needed, so I'd like to remove it.

In addition to removing the extends() operator, this PR turns on Babel preset-env's "targets": "defaults" option, which enables other syntax modernization: const instead of var and a fat arrow function instead of a function (which also makes the overall file more compact). These changes are not as important to me but they also clean things up, at the slight cost of changing the indentation of every line in the file.

Before: 3,102,133 bytes for 2,320 items
After: 2,179,463 bytes for 2,320 items

The change to the babel config is isolated in commit dbdf7b8 - the rest is just from running npm run build after making that change. Only the .js files are affected - no changes to .svg nor .jsx.

See also #3284 which makes a similar change for Paragon overall.

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[openedx-webhooks]

Thanks for the pull request, @bradenmacdonald!

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.31%. Comparing base (fc888d5) to head (41b9fcf).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3283   +/-   ##
=======================================
  Coverage   93.31%   93.31%           
=======================================
  Files         249      249           
  Lines        4441     4441           
  Branches     1014     1014           
=======================================
  Hits         4144     4144           
  Misses        294      294           
  Partials        3        3           

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