fix: better tree shaking with @carbon/icons-react and carbon-react-components

[jhpedemonte]

What do these changes do/fix?

Slightly updated version of #208.

Fixes #202

How do you test/verify these changes?

Compare building the example app with and without these changes:

Building from master:

  874.61 KB    build/static/js/2.45b3be80.chunk.js
  25.52 KB     build/static/css/main.0f5e9c85.chunk.css
  1.93 KB      build/static/js/main.97b18a0f.chunk.js
  785 B        build/static/js/runtime-main.6c9e6b2e.js

Building with this PR:

  508.65 KB (-365.96 KB)  build/static/js/2.523141c6.chunk.js
  25.52 KB                build/static/css/main.0f5e9c85.chunk.css
  1.92 KB (-7 B)          build/static/js/main.d87ceb41.chunk.js
  785 B                   build/static/js/runtime-main.6c9e6b2e.js

Have you documented your changes (if necessary)?

Are there any breaking changes included in this pull request?

[jhpedemonte]

Build is failing during tests:

discovery-search-app: yarn run v1.22.11
discovery-search-app: $ yarn test:unit && yarn test:e2e
discovery-search-app: $ cross-env SKIP_PREFLIGHT_CHECK=true CI=1 react-scripts test --env=jsdom
discovery-search-app: FAIL src/__tests__/App.test.js
discovery-search-app:   ● Test suite failed to run
discovery-search-app:     /home/runner/work/discovery-components/discovery-components/node_modules/carbon-components-react/es/components/ListBox/index.js:7
discovery-search-app:     import * as _PropTypes from './ListBoxPropTypes';
discovery-search-app:     ^^^^^^
discovery-search-app:     SyntaxError: Cannot use import statement outside a module
discovery-search-app:        9 | var carbonComponents = require('carbon-components');
discovery-search-app:       10 | var carbonComponentsReact = require('carbon-components-react');
discovery-search-app:     > 11 | var ListBox = _interopDefault(require('carbon-components-react/es/components/ListBox'));
discovery-search-app:          |                               ^
discovery-search-app:       12 | var reactDom = require('react-dom');
discovery-search-app:       13 | var reactDom__default = _interopDefault(reactDom);
discovery-search-app:       14 |
discovery-search-app:       at ScriptTransformer._transformAndBuildScript (../../node_modules/@jest/transform/build/ScriptTransformer.js:537:17)
discovery-search-app:       at ScriptTransformer.transform (../../node_modules/@jest/transform/build/ScriptTransformer.js:579:25)
discovery-search-app:       at Object.<anonymous> (../../packages/discovery-react-components/dist/index.js:11:31)
discovery-search-app: Test Suites: 1 failed, 1 total

But when I run locally, it succeeds. Haven't been able to figure out why it's failing.

[jhpedemonte]

Fixed with guidance from facebook/create-react-app#9938 (comment)