test: verify importing js exports works before versioning

[skjalgepalg]

Use testpack-cli to pack and install repo in separate test-folder to verify js exports in preversion step.

• add new test script
  • imports icons, expressive variants, logos and previews to an mjs and js -file and logs the number of icons in each category
  • This will parse all the icons and fail if we attempt to ship invalid js syntax
  • Installs React for testpack-cli and does the above check for jsx exports as well.
    • Note that adding jsx exports will break the test-script for runs without the testpack-cli context
      • Uncertain if there is a way to make React available for running npm run test
  • Evaluates core-icons-iife.js into a jsdom instance and counts the number of children inside the generated <svg>-tag to verify that it runs as intended.
• Runs the test-script in a GitHub action

• Check CommonJS exports
• Check ESM exports
• Check CommonJS exports for React/JSX
• Check ESM exports for React/JSX
• Verify types
• Check large icons
• Check iife file

Note: this PR does not address jsx/react exports yet

[ajaco]

Ser fint ut for mine øyne det her, men mistenker en kommentar kan slettes